04 01 004%20 %20masterate%20dissertation

Document No: 04-01-004 - Masterate Dissertation

The Design Of A New Bed Adjustability Mechanism

Mark Adrian van Rij

A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering

December 2001

Manufacturing Systems Group Department of Mechanical Engineering

The University of Auckland

I

Abstract

The focus of this project was the development of a simple adjustable bed for the

home environment. Design Mobel, a Tauranga based flexible slat bed

manufacturer, initiated the project with the desire to develop an innovative and

inexpensive mechanism for their new Circadian bed range that would not require

an electrical supply.

The design was performed systematically using the Pahl and Beitz methodology

with a number of design techniques to aid the process. The opinions of the

targeted end user were gathered through a series of surveys and user trials which

were processed into practical engineering requirements using the QFD technique.

Patents and products in the area of adjustable beds were analysed to determine

the context and the features available. Objective trees and functional analysis

were also used to determine the direction of the project. All this information was

collated and processed into the Product Design Specification (PDS) containing

the entire list of requirements essential from the end product.

Once the design requirements were determined a series of concepts were

developed with the aid of brainstorming sessions, synectics sessions, and the

morphological matrix technique. The principle solution was selected from these

concepts using the weighted objectives technique. A pneumatic concept was

investigated as the method of actuation but was later dropped when it proved to

be unviable. The final choice of actuator, which went against the initial

objectives, was an off the shelf electric actuator that had been developed

specifically for the adjustable bed market.

The final design uses Dewert’s Duomat double electric motor actuator to move

the top and bottom adjustable sections. A five bar linkage mechanism delivers a

combined back and head adjustment while the bent leg adjustment is achieved

with a four bar linkage mechanism. The concept was developed up until the

Abstract

II

beginning of the detail design phase where subsequent work will be performed

for production and final release into the market place in August 2002.

III

Acknowledgements

There are many individuals who have contributed to the success of this thesis,

without their support this simply would not have been possible. I would like to

take this opportunity to thank them for their contributions.

I am very thankful to Dr. Enrico Hämmerle for his assistance. His advice,

guidance and encouragement was invaluable.

The department of Mechanical Engineering and the Manufacturing

Systems group for their resources and assistance.

The staff and students in the Manufacturing Systems Laboratory,

particularly Dr. Xun Xu, Ken, Adam, Vijay, and Ludo for their friendship

and support.

Tim Allan from Design Mobel for establishing the project, passing on

valuable knowledge, and his subsequent supervision and direction

throughout my research.

The Design Mobel Team, including: Nik, Greg, Cory and Karla for

assisting ‘the Rij Man’ in his quest to conquer the world.

For all my friends who encouraged me throughout the highs and lows, in

particular Tyler McMillan and David Baldwin. Special thanks to Angela

Renz, Megan Sandford, and Rajneesh Agnihotri for ironing out the kinks

in my work in its final stages.

Pete Maslin for his friendship and camaraderie during the year, and

sharing in sleepless nights as we tackled our theses together.

The Clarks, the Brownings and the flat in Windsor St for being so

hospitable to me during the last year.

To my family for being a continual source of love and prayer support.

Especially to Dad and Julie for the many hours of editing and proofing.

The Foundation for Research, Science and Technology NZ Ltd for the

financial support of this project.

IV

Contents

Abstract I

Acknowledgements ....................................................................................................III

Contents IV

List of Figures VII

List of Tables X

List of Abbreviations...............................................................................................XIII

1 Introduction .......................................................................................................... 1

1.1 Adjustable Beds ........................................................................................... 1

1.2 Design Mobel ............................................................................................... 3

1.3 Project Aim................................................................................................... 3

1.4 Thesis Layout............................................................................................... 4

2 Background to a Systematic Approach to Design......................................... 5

2.1 Systematic Design ....................................................................................... 6

2.2 Design Techniques ...................................................................................... 7

2.3 Models of Systematic Design................................................................... 12

2.4 The Four Phases of Prescriptive Design Models .................................. 13

3 The Design Proposal......................................................................................... 24

3.1 The Brief...................................................................................................... 24

3.2 Determining the Problem......................................................................... 24

3.3 Formalising The Design Brief.................................................................. 27

4 Approach to the Problem ................................................................................. 28

4.1 Design Focus.............................................................................................. 29

4.2 Clarifying the Task.................................................................................... 30

4.3 Conceptual Design.................................................................................... 31

4.4 Embodiment Design ................................................................................. 32

4.5 Detail Design.............................................................................................. 34

5 Determining the Design Requirements........................................................ 35

5.1 Background Information.......................................................................... 35

5.2 Customer Needs and Preferences........................................................... 44

Contents

V

5.3 Design Techniques .................................................................................... 53

6 Developing the Concepts................................................................................. 58

6.1 Brainstorming / Synectics Session ......................................................... 58

6.2 Searching for Working Principles........................................................... 61

6.3 Generating Alternatives ........................................................................... 62

6.4 Evaluating Alternatives............................................................................ 64

7 Embodiment of the Design.............................................................................. 67

7.1 Definition of the Bed Subassemblies ...................................................... 67

7.2 The Adjustability Mechanism ................................................................. 69

7.3 Actuation .................................................................................................... 77

7.4 The Bed Features ....................................................................................... 82

7.5 Back Mechanism........................................................................................ 89

7.6 Leg Mechanism.......................................................................................... 92

7.7 Summary .................................................................................................... 94

8 Prototype 95

8.1 Problems to Overcome in the Making of the Prototype...................... 95

8.2 Prototype User Trial ................................................................................. 97

8.3 Design Review......................................................................................... 104

9 Discussion......................................................................................................... 111

9.1 “Clarifying the Task” Step ..................................................................... 111

9.2 “Concept Design” Step........................................................................... 112

9.3 “Embodiment Design” Step .................................................................. 115

10 Conclusions ...................................................................................................... 118

11 References ......................................................................................................... 122

12 Bibliography..................................................................................................... 124

Appendix A Patent Analysis .............................................................................. 126

Appendix B Product Analysis ........................................................................... 127

Appendix C Adjustability Activities Questionnaire .................................... 129

Appendix D Adjustability Activities Survey Summary............................... 133

Appendix E Bed Adjustability User Trial........................................................... 134

Appendix F Function Structures....................................................................... 135

Contents

VI

Appendix G QFD.................................................................................................. 137

Appendix H PDS .................................................................................................. 142

Appendix I Morphological Matrix Method................................................... 146

Appendix J Evaluating Alternatives ............................................................... 153

Appendix K Prototype User Trial ..................................................................... 156

VII

List of Figures

Figure 1-1 The Franko Electro Lift SL1 (reproduced from KG 2000)................. 2

Figure 2-1 The Pahl and Beitz design process (1996) ......................................... 14

Figure 3-1 The break-up of the bed length into 330mm slat intervals............. 26

Figure 4-1 A time based distribution of each of the design phases ................. 28

Figure 5-1 Worst case weight distribution on the head, back and leg sections................................................................................................... 43

Figure 5-2 A sample screen shot of the Ergo Check software results.............. 44

Figure 5-3 Photo showing a participant being tested in the adjustability user trial ................................................................................................. 51

Figure 5-4 General function structure for the adjustability mechanism ........ 53

Figure 5-6 QFD Chart 19/3/01.............................................................................. 56

Figure 6-1 Top and bottom half adjustment options ......................................... 65

Figure 6-2 The level of adjustability initially pursued....................................... 66

Figure 6-3 The final breakdown of the adjustability.......................................... 66

Figure 7-1 The arrangement of the slats and shoes in the bed frame .............. 67

Figure 7-2 The Circadian bed frame that cradles the adjustability mechanism............................................................................................. 68

Figure 7-3 Elevations of the side rail and end rail .............................................. 68

Figure 7-4 The break up of the bed length into 330mm zones ......................... 68

Figure 7-5 The final arrangement of the roller concept ..................................... 70

Figure 7-6 Strut arrangements (i) flat sheet or (ii) extrusion............................. 70

Figure 7-7 Roller wheel running on the underside of the adjustable rail ....... 71

Figure 7-8 The motion of the slide back carriage system .................................. 72

Figure 7-9 Slide back patent (WO9730614A1)..................................................... 72

Figure 7-10 Positioning of the adjustable rail groove so that the slats sit inline along the length of the bed ...................................................... 73

Figure 7-11 The adjustable frame showing the pivot points and cross bars ......................................................................................................... 73

Figure 7-12 One crossbar is welded to the inside of the parallel adjustable rails at the end furthest from the mounting end .......... 74

List of Figures

VIII

Figure 7-13 Top view of frame showing the buttocks section mounted in the bed frame and the two sizes of slats ........................................... 74

Figure 7-14 The adjustable frames being assembled with a cradle frame ........ 75

Figure 7-15 Cross section view showing the interference of the slats as the back section is raised ..................................................................... 76

Figure 7-16 The modified back mechanism with reduced angle and clearance requirements........................................................................ 76

Figure 7-17 The layout of the Franko lift plus system ......................................... 77

Figure 7-18 A selection of different actuators showing the difference in shape and form ..................................................................................... 80

Figure 7-19 The Dewert linear actuators (reproduced from Dewert (2001)) ..................................................................................................... 80

Figure 7-20 Linak Rotational Actuator (Reproduced from Linak (2001)) ......... 81

Figure 7-21 The Dewert Duomat actuator (reproduced from Dewert (2001)) ..................................................................................................... 81

Figure 7-22 The leg hinge concept slotting into the adjustable rail ................... 82

Figure 7-23 Pivoting about the end of the rail causes interference .................... 83

Figure 7-24 The rail can be cut away to stop interference................................... 83

Figure 7-25 Bottom pivoting for knee joint............................................................ 83

Figure 7-26 Top pivoting for back and thigh joint ............................................... 83

Figure 7-27 Pivot bracket used to mount the cross tube below the level of the frame ........................................................................................... 84

Figure 7-28 Pivot bracket that fastens directly to the sidewall to mount the cross tube within the height of the bed frame ........................... 84

Figure 7-29 Mounting the cross tube directly into the bed frame side wall ......................................................................................................... 85

Figure 7-30 Schematic of the bed frame side rail .................................................. 85

Figure 7-31 Rivnut in a thin wall sheet .................................................................. 86

Figure 7-32 Plate bracket for mounting devices to the bed frame ..................... 86

Figure 7-33 The aircraft fastener is riveted to the aluminium sheet .................. 87

Figure 7-34 Example of pivot mounting using a bolt and bush arrangement .......................................................................................... 87

Figure 7-35 Adjustable rail attachment fastener ................................................... 88

List of Figures

IX

Figure 7-36 Mounting the actuator clevis with a yoke attachment.................... 88

Figure 7-37 The location of the stopper I relation to the fixed buttocks............ 89

Figure 7-38 Head section movement...................................................................... 90

Figure 7-39 The movement of the peg in the head hinge .................................... 90

Figure 7-40 Screen shot of the kinematics software 5-Bar................................... 91

Figure 7-41 Back pivot and cross rail...................................................................... 91

Figure 7-42 The final configuration of the back mechanism............................... 92

Figure 7-43 Leg 4 bar mechanism concept............................................................. 92

Figure 7-44 The final design of the leg hinge ........................................................ 93

Figure 7-45 The final configuration of the leg mechanism.................................. 93

Figure 7-46 A rendered CAD model of the adjustable bed................................. 94

Figure 8-1 The desired adjustable rail extrusion ................................................ 96

Figure 8-2 The final solution for the prototype adjustable rail......................... 96

Figure 8-3 Single piece aluminium hinge ............................................................ 96

Figure 8-4 QFD chart 29/10/01........................................................................... 105

Figure 8-5 Photo of the fully adjusted bed with mattress ............................... 108

Figure 8-6 Photo of the bed with a subject testing the adjustment ................ 108

Figure 8-7 Photo of the fully adjusted mechanism........................................... 109

Figure 8-8 Side on photo of the fully adjusted mechanism............................. 109

Figure 8-9 Close up photo of the prototype leg adjustment with mattress................................................................................................ 110

Figure 8-10 Close up photo of the prototype leg hinge ..................................... 110

X

List of Tables

Table 4-1 The design techniques used at each step of the design process.................................................................................................... 28

Table 5-1 Different types of devices covered in the adjustable bed patents .................................................................................................... 37

Table 5-2 Proportions of the patents designed for the hospital and the home....................................................................................................... 37

Table 5-3 Percentages of the different actuation methods used in the bed patents ............................................................................................ 37

Table 5-4 Percentages of the different adjustment mechanisms in the patents .................................................................................................... 38

Table 5-5 Percentages of the bed patents with height adjustment ................. 38

Table 5-6 Proportions of the patents providing adjustment at each of the body zones of the bed.................................................................... 39

Table 5-7 Features of the patented adjustable beds.......................................... 39

Table 5-8 The method and level of adjustment available in the products ................................................................................................. 41

Table 5-9 Proportions of the different remote control adjustment methods.................................................................................................. 41

Table 5-10 Features available in the adjustable beds.......................................... 41

Table 5-11 The mass on each bed zone and groups of zones under the worst load case...................................................................................... 42

Table 5-12 Number and sex of the adjustable activity survey respondents ........................................................................................... 45

Table 5-13 Age distribution of the respondents to the adjustable activity survey....................................................................................... 45

Table 5-14 Pleasure, frequency and ease of performing the activities in bed .......................................................................................................... 46

Table 5-15 Summary of the participants opinions of performing each of the activities........................................................................................... 47

Table 5-16 Respondents who prop themselves up in bed and for what activities ................................................................................................. 48

Table 5-17 Respondents satisfaction of propping themselves up in bed ........ 48

List of Tables

XI

Table 5-18 Respondents desire for independently adjustable halves of the bed.................................................................................................... 48

Table 5-19 Level of adjustability desired by the participants ........................... 49

Table 5-20 Total number of males and females in the user trial....................... 50

Table 5-21 Distribution of female participants based on height and weight..................................................................................................... 50

Table 5-22 Distribution of male participants based on height and weight..................................................................................................... 50

Table 5-23 Ratings and angles given by the participants for each activity.................................................................................................... 52

Table 5-24 Participants average ratings from the post questionnaire.............. 52

Table 6-1 The possible means to achieve each of the features and functions ................................................................................................ 63

Table 6-2 Summary of the concept groups generated in the morphological matrix .......................................................................... 64

Table 6-3 A ranked summary of the utility values assigned to each concept ................................................................................................... 65

Table 8-1 The number of male and female participants in the user trial ...... 98

Table 8-2 Pre-Questionnaire average ratings .................................................... 99

Table 8-3 The results of performing the three activities in the flat and adjusted configurations ..................................................................... 101

Table 8-4 The proportions of participants who set the desired position to the maximum allowable back and leg angles............................ 102

Table 8-5 Post Questionnaire results ................................................................ 103

Table G-1 Evaluation of the attributes of a standard bed and the Dico Adjustable bed .................................................................................... 138

Table G-2 Engineering characteristics required for each of the requirements ....................................................................................... 139

Table H-1 The PDS document issued on 10/10/2001 ..................................... 142

Table I-1 List of all the possible means to achieve each of the features and functions....................................................................................... 147

Table I-2 Morphological list of feasible solutions for each of the features and functions....................................................................................... 148

Table J-1 Design objectives.................................................................................... 153

List of Tables

XII

Table J-2 Scores for each of the objectives........................................................... 154

Table J-3 Objectives ranked in order and given weightings ............................ 154

Table J-4 The performance parameters for each of the objectives................... 155

XIII

List of Abbreviations

ABET Accreditation Board for Engineering and Technology

CAD Computer Aided Drawing

CAM Computer Aided Manufacturing

EMC Electromagnetic Compatibility

ESD Electrostatic Discharge

FEA Finite Element Analysis

PDS Product Design Specification

QFD Quality Function Deployment

SEED Sharing Experience in Engineering Design

1

1 Introduction

This chapter presents the design project that was proposed by Design Mobel

including the desired aims and the approach taken to achieve these. The chapter

begins with a brief description of adjustable beds to put the problem into context.

Finally, the structure of the report is disclosed with an outline of the way in

which the project was performed.

1.1 Adjustable Beds

As long as people have slept in beds there have been continual attempts to revise

their construction in order to better accommodate the individual’s particular

needs for sleeping and lounging in comfort. One major initiative, which is used

extensively in the health sector, was the development of the adjustable bed.

Adjustable beds were originally designed with the principal purpose to

accommodate the patient in a variety of positions. These “hospital-type” beds

are generally unattractive, complex, and too expensive for use in the home

environment.

A growing number of people place television and other media based

entertainment devices in their bedrooms, and spend more time lounging in bed.

For this to be enjoyable issues of posture are important. Consequently companies

are taking a scientific approach to bed design with these needs in mind and with

the intention of solving the inadequacies in regard to such things as comfort

when sleeping or reading. The result has been the development of adjustable

beds for use in residential environments by those who have no health or physical

impairment. The adjustable bed is now considered by many to be an alternative

piece of leisure furniture (Stroud 2000). An example of a modern adjustable bed

for the home is shown in Figure 1-1.

Introduction

2

Figure 1-1 The Franko Electro Lift SL1 (reproduced from KG 2000)

These adjustable beds can usually be moved from a fully reclining position to a

sitting-up position in which at least one section is tilted up to provide a back rest.

The body is supported by a series of adjustable sections that are hinged or

pivotally connected together. The body support sections are mounted on a bed

frame and are moved relative to each other and the frame to obtain the various

positions.

The adjustment of the bed is either manual or powered. Manual beds require

human effort to move the adjustable sections of the bed to the desired attitude

and height, whereas powered beds use motors or actuators to perform the same

result. Manual beds are less expensive than powered beds, largely due to being

less complicated in construction. However, they are difficult to use and

somewhat awkward as they have to be operated from outside the bed using

some effort which is especially relevant if the person is incapacitated. In contrast,

powered beds are convenient and can be operated with ease by those who are

bedridden. Despite the advantages of adjustable beds they are more complicated

in construction than conventional beds, and therefore, are generally more

expensive, as well as being more difficult to disassemble, transport and

reassemble.

Introduction

3

1.2 Design Mobel

Design Mobel is a Tauranga based designer, manufacturer, and marketer of fine

quality furniture, whose reputation for quality has led them to be recognised as

the leading brand in the flexible slat bed market in New Zealand. They pride

themselves on using state of the art technology and innovative production

methods. This is reflected in the broad base of skills present in the design team,

from graphic design, architecture, textiles, CAD/CAM to industrial design.

In early 2000 Design Mobel approached the Mechanical Engineering Department

at Auckland University for assistance in developing a new product for their

flexible slat bed range called the Circadian system. Their intention was to extend

their product range to introduce an adjustable slat bed into the New Zealand

market for the home environment. At the time there was no New Zealand

producer of such an item. Their intention was not to target those who were

unwell or convalescing at home but rather those who want to enhance their

bedtime leisure. The general brief presented by Design Mobel incorporated the

design of a simple and affordable adjustable mechanism to integrate into the

frame of their latest bed range.

Design Mobel were aware that the mechanism required to produce the

adjustment was available through third party suppliers and could be retrofitted

to their bed. However, these mechanisms did not have the desired styling, and

integration into their frame would have required extensive modifications to the

bed. Therefore, Design Mobel made the decision to design their own mechanism.

1.3 Project Aim

The overall aims of the master’s project was to:

• Design a bed adjustability mechanism within the requirements set out by

Design Mobel

• Identify design methodologies best suited to the project

Introduction

4

• Determine whether the methodology could be applied to other settings

Instead of just determining the most appropriate direction of the design based on

‘gut feeling’ or pragmatics, which has serious limitations, the design process was

to be undertaken in a systematic manner. By taking a systematic approach the

most appropriate design methodologies and aids would be discovered. Pahl and

Beitz (1996) suggest that by taking a deliberate step-by-step approach to design,

nothing essential is overlooked. This methodical style of practice is viewed as

indispensable when executing original designs. There is a general belief that

systematic design stifles your creative ability and therefore the challenge was to

be able to show that by using the systematic approach to design methodology

and design tools that an efficient and superior design would result.

1.4 Thesis Layout

The purpose of this thesis is to describe in detail both the process involved in

designing the adjustable bed system and to describe the mechanism that resulted.

This dissertation begins by outlining the background research that was carried

out into systematic design, and the design process. The report then discusses the

design brief and the approach to be taken in response to Design Mobel’s project

objectives. The processes taken to determine the design requirements are

described and are followed by the concept development and evaluation. The

embodiment design process steps and decisions are listed with a chapter

exploring the development of the resulting prototype and the design changes

required for production. The final section discusses the issues that arose

regarding the systematic approach with recommendations for completing the

detail design for production.

5

2 Background to a Systematic Approach to Design

Engineering design is not something that is easily defined. Hyman (1998)

suggests that there appears to be no common definition for engineering design

except that it is a methodical approach to solving a particular class of problem.

This is suggested because a feature of much problem solving is that the solutions

are often arrived at without an awareness of the step involved in the process.

Suh (1990) describes it as being ‘a continuous interplay between what we want to

achieve and how we want to achieve it’. Other researchers ((Hales 1993) (Starkey

1992) (Lewis and Samuel 1989)) offer similar definitions that distinguish

engineering design as a process of recognising a need and creating a system to

satisfy that need.

Further helpful definitions of design are given by the Sharing Experience in

Engineering Design (SEED) and by the Accreditation Board for Engineering and

Technology (ABET).

The SEED definition suggests: ‘Engineering design is the total activity necessary

to establish and define solutions to problems not solved before, or provide new

solutions to problems which have been previously been solved in a different

way. The engineering designer uses intellectual ability to apply scientific

knowledge and ensures the product satisfies an agreed market need and product

design specification whilst permitting manufacture by the optimum method. The

design activity is not complete until the resulting product is in use providing an

acceptable level of performance and with clearly identified methods of disposal’

(Hurst 1999).

The ABET definition (1990) states that: ‘Engineering design is the process of

devising a system, component, or process to meet desired needs. It is a decision-

making process (often iterative), in which the basic sciences, mathematics, and

engineering sciences are applied to convert resources optimally to meet a stated

Background to a Systematic Approach to Design

6

objective. Among the fundamental elements of the design process are the

establishment of objectives and criteria, analysis, construction, testing, and

evaluation’.

Suh (1990) describes four components involved in the design process, each based

on engineering and scientific principles: the problem definition, the creative

process of generating a solution, the analytical process of determining if the

solution is suitable, and the ultimate check of fidelity of the design. While this is

true, the process of design often tends to be open ended with no readily

identifiable closure point. Hyman (1998) suggests that this process is continuous

until the cost of continuing the design process becomes greater than the benefits

of a further improvement in the design.

2.1 Systematic Design

The design process is clearly complex and has great potential for complications.

As in problem solving, the temptation is to take an undisciplined pragmatic

approach. Pahl and Beitz (1996) suggest that since design is such a creative

process if it is unguided the potential can be greatly limited. They recommend a

systematic approach to achieve this which involves following a design process

model which has a structured set of design phases with critical activities required

at each stage. Within each step of a systematic approach there will be a variety of

different design methods and techniques applied, and an awareness of these

allows the designer to engage and progress through a design problem more

proficiently.

The benefits of taking a systematic approach are claimed to include better design

solutions with improved quality and efficiencies, as well as providing a clear and

logical record of the development process for subsequent review and analysis.

Hales (1993) suggests this approach is more professional, which inspires greater

confidence from management and the customer, and provide quality solutions


7

within the constraints of the project. Adhering to such a process will free the

mind and allow more inventive and better-reasoned solutions to emerge. The

designer can then step back from the design and rely on the model knowing that

the key elements in the search for a design solution have not been overlooked

(Hyman 1998).

Systematic design is not a constraining process; instead it offers a framework in

which the designer has freedom to move about. Nor does it imply a step-by-step

serial process, or a series of instruction to follow blindly. The times spent on each

step and in which order they are performed is very much dependent on the

particular design problem. The ability for steps to be visited several times and

for designers to even unconsciously blend some of the steps together

demonstrates the flexibility of a systematic approach. Because the entire process

is subjective in nature, an infinite number of solutions are possible; right down to

individual designers defining a totally different set of design requirements for

the same perceived needs.

2.2 Design Techniques

Design techniques are tools or aids used for bringing a rational approach into the

design process and a designer may combine a number of these methods during

the course of the design process (Cross 1994). More often than not these design

techniques appear to be too systematic and are not useful in the chaotic world of

the design office. Furthermore they do not provide step-by-step instructions on

how to produce amazing ideas and they cannot replace the gifts of a talented

designer. Nevertheless, French (1971) suggests that they increase the size and

range of the projects the designer can undertake and improve the quality and

speed of their work.

Some of these techniques are common sense methods yet by formalising them

into the design process they are not over looked. At times by following a design


8

technique it may appear that the focus of the design process has been diverted

from the central task of designing. While this is true, this diversion is important

as it sometimes allows the designer to view a broader picture rather than viewing

an immediate problem at hand.

Formalization of the design method widens the approach to the problem,

externalises design thinking and encourages the designer to look beyond the first

solution that enters their head. Factors that otherwise may have been overlooked

with informal methods are not neglected in a more structured approach.

Externalisation is the process of transferring thoughts onto paper which is done

in a number of ways such as creating charts and diagrams. Cross (1994) suggests

that all of this frees the designers mind from the complexities of the design to

allow more intuitive and imaginative thinking. Using design techniques also

reduces the size of mental steps, prompts inventive steps, reduces the chances of

overlooking them, and generates design philosophies for the problem in question

(French 1971).

Types of Design Techniques

The design techniques used within a systematic approach can be broken into two

broad groups: creative methods and rational methods. Creative methods try to

increase the flow of ideas by removing the mental blocks that inhibit creativity, or

by widening the area in which the search for a solution is performed. There are

many creative methods, some examples of which are listed below:

• Brainstorming • Enlarging the search space • Analogy • Method 635 • Synectics • Gallery Method • Fantasy • Delphi Method

Rational methods encourage a systematic approach to design but also aim to

widen the search space for potential solutions, by facilitating teamwork and

group decision-making. There are several rational methods that cover aspects

from problem clarification to detail design:


9

• Quality Function Deployment • Function Analysis • Morphological Chart • Weighted Objectives • Value Engineering • Functional Cost Analysis • Objective Methods • Taguchi Method

Rational methods are often misunderstood as cramping the creativity but the

intentions of systematic design are to improve the quality of design decisions,

and hence the end product. They are not the opposite of creative methods, and

therefore the process is not one of ‘straight jacketing’ or stifling the creativity.

Cross (1994,) states that creative methods and rational methods are

complementary aspects of a systematic approach to design because they both

offer unique and equally important functions to the design process.

The following section describes in brief the creative and rational techniques that

were used in the design of the bed adjustability system.

Creative Design Techniques

Analogy

Analogy is a technique for suggesting solutions using stimulus from any source,

particularly from outside the field in which the problem originates. The analogy

may be as great as a direct transfer of a piece of equipment from one device to

another or much more subtle with the analogous situation providing only the

basic idea for the solution of quite a different form. Pugh (1991) states that

‘analogy is the most powerful tool in the area of idea stimulation and concept

generation’.

Brainstorming

Pugh (1991) suggests that brainstorming is the most widely utilised method of

idea generation. Alex F. Osborn first suggested brainstorming back in the 1950s.

He defined the verb ‘brainstorm’ as: ‘To practice, a technique by which a group

attempts to find a solution for a specific problem by amassing all the ideas

spontaneously contributed by its members’ Osborn (1963). Pahl and Beitz (1996)


10

describe brainstorming as a method of generating an inundation of new ideas

that may have been repressed or not considered in the present context utilising

the association of ideas and the stimulation of memory. Miracles should not be

expected from a brainstorming session as many of the ideas may not be

technically or economically feasible, and those that are will often be familiar to

the experts. The sessions are intended to trigger new ideas, and are not expected

to produce a complete solution, as most problems are far too complex and too

difficult to be solved with spontaneous ideas alone.

Synectics

Synectics is similar to brainstorming with the main difference being that its aim is

to trigger the flow of fresh ideas using analogies. These analogies are frequently

drawn from non-technical fields and everyday systems are examined for

relevance to the current problem area. Pahl and Beitz (1996) describe synectics as

the ‘activity of combining various and apparently independent concepts’ to

generate solutions that were previously overlooked. The method is much more

formal and systematic than brainstorming and much more time is spent

familiarising the team with the problem. Starkey and Cross (1992; 1994) suggest

the aim is to work towards a particular solution, concentrating on a single

analogy, in the hope of extracting one or more ideas of genuine relevance.

Rational Design Techniques

Objective Trees Method

The purpose of the Objective Trees Method is to help in the clarification of an ill-

defined problem that has been given to the designer. In the clarification of the

task it is helpful to develop a set of objectives that the design must meet. The

Objective Trees Method allows the designer to perform this task through

outlining the objectives under consideration in a diagrammatic form. The

objectives are listed in a hierarchical pattern with sub-objectives in order to show

how the objectives relate to one another.


11

Function Analysis

Function analysis helps to determine the essential functions that the device,

product, or system to be designed must satisfy, whatever physical components

might be used. The product is designated a ‘black box’ that contains all the

functions that are essential for converting the inputs into the desired outputs.

Weighted Objectives

When a set of alternative designs are created weighted objectives can be used to

choose between the alternatives in a rational procedure, rather than relying on

pure intuition. The evaluation is based on numerical weights assigned to the

objectives that need to be achieved by the design. These weighted objectives are

used to generate numerical scores that create a ranked list of the most promising

concepts.

Morphological Analysis

Morphological analysis involves generating a table of possible functional options

from which various combinations can be selected. This is particularly useful

when a system has several functions that need to be satisfied. Pahl and Beitz

(1996) suggest it is often useful to divide problems into sub-problems which can

be solved individually and then recombined in order to arrive at an overall

solution. To ensure that each of the potential combinations are covered a

morphological chart is drawn up. On the left hand side of the table all the

functions of the system are listed and opposite each are the possible methods of

achieving the principle solution. A combination is formed by picking out a

selection of options so that each function is satisfied. French (1992) adds that

some combinations may not make sense and it is not wise to expect miracle

solutions.


12

Quality Function Deployment (QFD)

When designing a product it is especially important to recognise that the person

who buys a product is the most important person in determining its commercial

success. The ‘voice of the customer’ should be a high priority in determining the

product’s attributes. Hales (1993) describes QFD as a systematic means for

identifying customer needs and translating them into appropriate engineering

characteristics and into a quantified design specification. The challenge that

Hurst (1999) lays down for the designer is to optimise the requirements for the

design while satisfying the customer need in the most cost effective way.

Value Analysis

Value analysis is used to make the designer conscious of the form that design and

production methods have over the economics of producing a component. The

major difference between value analysis and conventional cost cutting is the

involvement of reducing the cost while maintaining or improving the

functionality of the product. The process begins with an analysis of the

functionality of the component, from which alternatives are developed that

perform the function at the lowest cost within appropriate quality standards.

2.3 Models of Systematic Design

Design models can be grouped into two main types, descriptive and prescriptive.

Cross (1994) describes a descriptive model as solution based with the emphasis

on generating a solution early on in the process. Any flaws found in subsequent

analysis mean the concept is scrapped and a new concept generated to repeat the

cycle. The process is usually presented as a flow diagram with flow loops

showing the iterative process. The heuristic based approach uses ‘rules of

thumb’ and previous experience to lead the designer in a direction that may not

necessarily be successful (Cross 1994). Conversely, a prescriptive model tries to

encourage the designer to work in a design methodology that is more algorithmic

and systematic in nature. The focus is on generating a performance specification


13

so that the design problem is fully defined with no elements overlooked. The

generation of several alternative concepts is encouraged with the final choice

made with a rational selection of the alternative designs. The general

progression is analysis-synthesis-evaluation (Cross 1994).

One such system is the Pahl and Beitz (1996) method which is a highly

recommended methodology that has been used successfully by designers in all

areas of engineering. The system is valuable because it has a comprehensive

model that still retains some clarity unlike many other prescriptive models (Pugh

1991) and therefore was used as the methodology behind the development of this

design. The various stages of the Pahl and Beitz model are listed in Figure 2-1.

2.4 The Four Phases of Prescriptive Design Models

It is generally accepted in a prescriptive design model that the process is broken

down into the following phases: clarifying of the task, conceptual design,

embodiment design and detail design. Sometimes the embodiment phase is not

included so the conceptual and detail design phase are enlarged to cover its

tasks. The following section looks at each of the design phases in more detail and

describes the main focus and steps required.

Planning and Clarifying The Task

When a designer starts a project, more often than not the problem statement they

have received is very vague. The first responsibility stated by Lewis et al. and

Cross (1989; 1994) is that the designer must identify the problems that are not

explicitly stated in the brief given to them, but which are implicit in the brief once

it is deconstructed. Starkey (1992) points out that it is entirely counter-

productive to produce a design that nobody wants or that only partially satisfies

the needs of the end user.


14

Task, Market, Company, Economy

Plan and clarify the task:Analyse the market and the company situationFind and select product ideasFormulate a product proposalClarify the TaskElaborate a requirements list

Requirements list(Design Specification)

Develop the principle solution:Identify essential problemsEstablish function structuresSearch for working principles and working structuresCombine and firm up into concept variantsEvaluate against technical and economic criteria

Concept(Principle Solution)

Develop the construction structure:Preliminary form design, material selection and calcuationSelect best preliminary layoutsRefine and improve layoutsEvaluate against technical and economic criteria

Preliminary layout

Define the construction structure:Eliminate weak spotsCheck for errors, disturbing influences and minimum costsPrepare the preliminary parts list and production and assembly documents

Definitive layout

Prepare production and operating documents:Elaborate detail drawings and parts listsComplete production, assembly, transport and operating instructionsCheck all documents

Product documentation

Solution

Plan

ning

and

cla

rify

ing

the

task

Con

cept

ual D

esig

nEm

bodi

men

t des

ign

Det

ail D

esig

n

Figure 2-1 The Pahl and Beitz design process (1996)


15

The purpose of this phase is to collect information on the requirements that have

to be fulfilled by the product and on the constraints that may arise. This begins

with the creation of a design brief that lists the general properties required by the

product. Various techniques are used to determine the function of the product

and the system boundary of the new design. These activities lead to the

formulation of a requirements list of the design, the product design specification

(PDS). The subsequent phases are based on this ‘living’ document that is

continually being updated as more information is gathered.

Design Brief

At this early stage of the design target objectives should be set, as it is unknown

which objectives can be met and to what degree. As the process proceeds it

becomes clearer which specific design will satisfy the users needs and as a result

the objectives can become much more specific (Love 1986). The orientation

changes from one of how, to one of what.

The first step in the design process is to develop a comprehensive design brief

from the information provided. The brief consists of general statements

regarding the essential goals that have to be fulfilled to satisfy the customer.

Hyman (1998) suggests using a structured framework to overcome the balance of

being too specific or too narrow by using three components: goals, objectives and

constraints. A goal is a response to the need, an ideal that may not be

accomplished. An objective is a quantifiable expectation of performance and

constraints define the permissible range of the design and performance

parameters.

Product Design Specification (PDS)

Cross (1994) suggests that performance specifications are statements of what a

design must achieve or do and are different to objectives in that they are defined

in terms of precise limits. These performance specifications are created in a


16

Product Design Specification (PDS) using the performance specification method,

which emphasises the performance required rather than the physical components

to achieve this operation. The intention is to define the problem while leaving an

appropriate amount of freedom for the designer to develop ways of achieving a

satisfactory design solution.

The definition Pugh (1991) gives for a PDS is ‘an evolutionary, comprehensively

written document that upon completion of the design should have evolved to

match the characteristics of the final product’. The PDS represents a widespread

list of constraints on the design context and can be described as a formal

document interfacing between marketing and engineering functions. The

perceived market needs are converted into functions and constraints covering the

products design, manufacture and marketability.

The performance specification is made up of demands and wishes. Demands are

requirements that must be met under all circumstances or the proposed solution

is not acceptable. Wishes are requirements that should be considered where

possible but dropped when they break some sort of stipulation such as increases

in cost.

As the design proceeds the specifications of the product become more detailed

but the objectives increase in size or scope. A performance specification limits

the range of acceptable solutions. However, as it sets the target scope for the

design it should not be defined too narrowly. A performance specification that is

too narrow may mean that acceptable solutions will be eliminated unnecessarily,

and too broad a specification will give little direction for the designer to aim at.

At this early stage it may not be possible to finalise every detail but Hales (1993)

states that the process of obtaining the approval for these may help to identify

specific items that have been left unresolved and the correct allowances can be


17

made for them. Once the loose goal has been established, more detailed

specifications can be drawn up. Lewis and Samuel (1989) state that the feedback

that comes from new information helps to refine the objectives so it becomes

clear where there are difficulties in satisfying conflicting objectives and the

nature of the compromises to be made emerge.

The task clarification process is a convergent phase, where the weaker ideas are

weeded out and the most promising are given more attention (Hales 1993) Once

the design problem has been defined and the requirements listed in the form of a

design specification, a firm base has been established for the remaining design

stages to proceed from. The problems may be solved and the concepts that result

can be evaluated against the design specification. No attempt should be made to

create any solutions until a first draft of a PDS has been developed. Sometimes

this is not possible since the design process is iterative and the PDS may be

considered a fluid document, which developed along with the design.

Conceptual Design

Once the design specification has developed sufficient information, the designer

is ready to being the creative work of giving substance to the product. The

convergent thinking of the task clarification is changed to divergent during the

conceptual phase, which involves broadening out to collect as many ideas as

possible. The conceptual design phase is mainly concerned with creating

solutions to the need established in the PDS. It is this phase of design that places

the greatest demands on the designer and where there is the most scope for

striking improvements. French (1971) suggests that this stage is where the most

important design decisions are made and requires the practical knowledge of

engineering science, production methods, and commercial aspects.

The problem statement is taken and broad solutions in the form of concept

schemes are created. The diverse range of solutions that are developed then have


18

to be evaluated and reduced down to the most appropriate concept, the principle

solution. The conceptual phase consists of two major cyclical components; the

synthesis of solutions to meet the need and the evaluation of these to determine

the one that is the most appropriate in terms with the PDS (Pugh 1991). Pugh

also recommends that the outcome of this phase should be a comprehensively

engineered concept that the embodiment phase can be established upon.

Generating Ideas

In generating solutions to an acceptable level, the knowledge base of technology

and engineering specific to the product area must be enlarged. Ideas have to be

produced in as much abundance as possible because single solutions usually lead

to a disaster. These ideas must also be developed to a level that is complete and

recognisable, and most importantly, in balance with the laws of nature. This

involves performing appropriate calculations in order to justify the particular

concept.

Ideas may have already been collected from earlier thinking or other products

may be available that have suitable features that can be incorporated into

possible solutions. Ideas may also be generated through systematic literature

and patents searches. It is also recommended to use some of the relevant design

methods discussed earlier, such as brainstorming, and morphological charts to

help synthesise new ideas. Pugh (1991) suggests that some of the most valuable

inspirations come from bouncing ideas off others to encourage the generation of

new ideas and improve existing ones. The possibility of producing a suitable

concept at the outset is unlikely and it is much more probable that there will be

several iterations of the process before something suitable is produced. It takes

some effort to bring the alternatives to the same level of development and detail

before any evaluation can take place.


19

An important part of the conceptual design phase is being able to communicate

the ideas. This can be done graphically, diagrammatically, verbally and through

modelling. Free hand sketches are very important and they may contain

suggestions of key features such as overall form, loads, and operational

conditions. Hyman (1998) suggests that the designer’s thoughts about possible

materials, size, and other features may come together and should be jotted down

with the pictorial representation. The concept sketches should be of sufficient

clarity to be understood by not only the designer but also those who will be

evaluating them.

The design phases should be followed systematically, but not necessarily rigidly.

If a brilliant concept is developed that does not satisfy the PDS, the problem may

lie with the PDS being to narrow or broad in focus. In this case, (Pugh 1991)

suggests the designer should re-evaluate the PDS and modify it if required since

as stated earlier, the PDS itself is evolutionary. The temptation to ‘cut and run’

with ideas before a full spectrum has been covered or the specification has been

fully developed should be avoided at all costs as the results may not be

satisfactory.

Selecting and Evaluating Concepts

With a series of concepts produced, the next stage of the conceptual design phase

involves selecting and evaluating the concepts using a convergent mindset. The

aim is to reduce the number of generated concepts to a short list of two or three

for further detailed analysis. Hurst (1999) states that it is clearly impracticable to

examine every concept in depth, but with only a small number of promising

concepts the process can be increasingly straightforward. The concepts should

conform to the requirements of the specification but each has to be critically

examined to test its suitability as a solution. Starkey (1992) suggests that a mini-

feasibility study of each alternative is required with the aim at either eliminating

or passing a concept for the final solution. When a selection is made there has to


20

be a justification for the choice, particularly regarding those that have been

discarded.

Some people are particularly good at creating new ideas yet having the ability to

discern the most promising option is a skill in its self. Designing by ‘gut feeling’

is a risky approach to take, as it is easy to favour one concept over another

because one factor seems to stand out, however the other negative factors are

often overlooked. Even a simple problem contains underlying factors, which are

difficult to weight against each other during a subjective assessment. If an

inappropriate design is chosen, there is little that can salvage the project once the

design process is initiated. Often the designer involved is bias in their opinion

and therefore an impartial decision is not always possible. Sometimes it is useful

to involve a group of individuals in the decision process to avoid these biased

judgements.

Thus the adoption of a systematic decision-making procedure is essential for

students and the most experienced designers alike during concept selection.

Pugh (1991) recommends that a set of criteria be established to evaluate the

concepts effectively. There are many structured procedures available for the

selection and evaluation of alternative concepts and these tools aid in creativity

in the context of controlled convergence.

Embodiment Design

Embodiment design builds on the principle solution selected in the conceptual

phase. The aim of this phase is to develop more detailed layouts of the concepts

and to resolve overall geometrical, dynamic, and safety issues. In contrast to

conceptual design the process is iterative in nature so analysis and synthesis are

used complementarily during the many corrective steps (Pahl and Beitz 1996).


21

Once a concept takes shape there is a large emphasis on optimisation of the

design, which is accomplished by what Hurst (1999) describes as ‘attacking what

are perceived to be the weak points of the design’. The embodiment phase is

described as the bridge between conceptual and detail design phases. This is

because there is a significant jump between the visualisation of an abstract

concept and the manufacturing of a safe and reliable product. Advancement

without sufficient and appropriate thought and development will usually result

in design failure.

The input to this phase is usually not more than a sketch and a PDS document.

The aim is to refine this initial information and develop it to the point where the

detail design and production planning can commence. This will consist of

definitive scheme drawings with accompanied documentation of calculations,

tolerances, suggested materials and manufacturing processes. Quite often the

embodiment phase will involve the production of a prototype that can be put

through a rigorous test program to validate the design.

Design considerations

There are many things to consider in the embodiment of a design. Hales (1993)

suggests that the design should be as simple and clear as possible as this has

many advantages in the manufacture, assembly, and cost of the final product.

Function, cost, and safety are paramount in the design process but the

appearance of an object is also a major factor in the appeal to the customer. An

engineering design with good aesthetics will be pleasing to the eye and give the

visual impression of functional efficiently.

The embodiment phase involves a significant amount of iterative design. The

process starts with a decision being made on the overall layout, which is then

modelled, analysed, synthesised, and optimised. A revised layout is then


22

produced which may have more detail or a modified feature. This whole process

is repeated many times until the best compromise can be made.

Hurst (1999) describes the early stages as the period when the most important

components are given size and strengths. Once the body and shape begin to

emerge the modelling, and synthesis can begin. Scheme drawings should be

created to show the motion, adequate clearances, and other information

concerning such subjects as tolerances and materials. These drawings should be

regularly updated and modified to reflect any changes made.

Material and process selection is an integral part of the engineering design

making process. The proper selection will lead to increased product

performance, greater efficiency, and reduced costs. Decisions made in this phase

dictate manufacturing processes and therefore it is important that throughout the

process advice is sought from manufacturing experts so that the designer can

attempt to utilise existing machinery and tooling where possible. The number of

components should also be optimised so that the least number of parts are used,

while at the same time not increasing their complexity beyond what is suitable.

Whenever possible it is generally more economical and practical to buy ready

made assemblies and components.

Calculations are essential in this phase of the design and many are usually

required. Hales (1993) suggests that the calculations should be carried out and

recorded for later reference with annotation and documentation so that other

engineers can easily understand them.

Detail Design

The final stage of the design process has been reached, whereby important

decisions have been finalised and what is now required is simply fine-tuning.

This involves focusing in at each of the embodied components and optimising


23

them. The design of each component has to be verified and information

regarding the manufacture should be completed. Detail design is generally more

concerned with the design of the subsystem and components that make up the

final design. As with all stages of the design this should be done within the

constraints of the PDS. The detail design process needs the harnessing of many

different areas of knowledge: materials, techniques of analysis, technology of the

situation, environment of the component, quantity, life, loading, aesthetic appeal,

and so forth (Pugh 1991). The input to the phase is the design intent and scheme

drawings, with the output being a series of detailed drawings and accompanying

documentation.

Further design decisions will be made and these will understandably influence

other areas of the design. As with the embodiment design it is iterative in nature

and the different design stages are continually overlapping. It is for clarity and

convenience that the distinction between the phases has been made. Throughout

the design process the designer becomes increasingly involved with the details of

the product, especially as it converges towards the best solution.

All stages of the design process are important and detail design is no exception.

The final stage of the design process is crucial in communicating the finer details

of a design and should not be left as an afterthought. According to Pugh (1991)

most accidents and disasters involving engineering design issues can be traced

back to errors from inexperience or poor judgement in detail design. Every

activity concerned with detail design is important to preserve and enhance the

design work that has already been achieved. If the details are not handled

conscientiously and professionally, all the hours of analysis and evaluation that

have preceded this point can be nullified, and the benefits of the well design

product can be lost

24

3 The Design Proposal

The following chapter discusses the proposal presented by Design, listing the

major constraints specified from the onset of the project.

3.1 The Brief

The initial brief presented for the design of the adjustability mechanism was

presented in writing, as shown below.

Aim: To develop a simple mechanism or means of adjustability integrated into

the bed frame. This mechanism would allow in bed adjustment and be focused

on providing additional features for activities in bed rather than purely

convalescing.

This brief was less than adequate and far too broad to determine the direction of

the design. The written documentation was further expanded through verbal

communication with the Design Mobel design team to pin down the exact

requirements desired.

3.2 Determining the Problem

As the investigations were made to determine the true nature of the project, a

great deal of information surfaced. There were significant constraints on the

project from dimensioning and volume limitations, to materials and aesthetic

form restrictions. The time plan involved developing a full working prototype

by the end of 2001, with subsequent detail design developing the product for

production release in mid 2002.

The design team presented a series of brochures of products currently available

on the market in the area of adjustable beds. The desire was for the information

to be analysed to establish the context of the design. Another requirement for the

The Design Proposal

25

designer was to perform research into the ergonomics of adjustable beds to

ensure the design would be ergonomically sound.

One requirement stipulated from the beginning was that the adjustment would

have to be performed with little effort to the user while lying in the bed. It was

also hoped that the method of moving the system would be something quite

innovative. Most systems use some sort of electric actuation to move the sections

but there is much discontent in Europe over having electrical devices producing

electromagnetic waves in the bed. Design Mobel’s desire was that the final

product be electricity free which would open it to a much larger market of

potential customers.

Other adjustable beds available overseas are very utilitarian, performing the

desired function with little consideration for style and grace. Design Mobel

invests quite strongly in developing furniture that is at the cutting edge of style

and this can be clearly seen in the Circadian system. To assimilate the

adjustability mechanism into the system it had to be simple, sleek, and

innovative.

The target market for the product is for use within the home, rather than a

hospital or rest home where adjustable beds are traditionally used. The bed will

be used for assisting activities such as reading and watching television, rather

than aiding in the treatment of patients. Subsequently the target user’s capacity

to invest in such a bed is significantly lower, compared with a hospital or rest

home. However, this is easily resolved as the requirements for health and safety

standards, added function, and robustness are greatly reduced in the home

environment, and therefore production costs are lower. The suggested cost price

per single side of the bed was set in the range of $250-400 with the aim obviously

for the lower end of the price bracket.

The Design Proposal

26

A major constraint was with the current method of grouping the slats that had

been developed for the Circadian system. The slats come in 330mm groups with

the choice of having three, four, or five slats in each zone. The zones cannot be

broken up so the articulation points of the adjustability mechanism are set at

these 330mm intervals as shown in Figure 3-1.

Figure 3-1 The break-up of the bed length into 330mm slat intervals

When the system is up-graded to a double bed several issues arise. Clearly it is

not desirable to have one occupant trying to sleep while the other is reading with

the bed in an adjusted position. Therefore, the two sides of the bed must be

independent of each other, something which is particularly common with the

other products available on the market. This of course creates additional

problems such as separate mattresses and linen issues, yet it appears to be

unavoidable and a compromise must be met, as is reflected in other adjustable

products on the market.

Design Mobel had performed research into the design of mattresses for the

Circadian system and the technology would carry over to the adjustable variation

with minor changes. Consequently the design of the mattress is outside the

scope of this project.

Design Mobel desired a single solution to the problem they had presented but

there was confidence that a few other suitable alternatives may be devised. Of

the alternatives that were presented several were deemed unviable at the time,

however as the market for adjustable beds develops and manufacturing

limitations are reduced, the ability to pursue these in the future is increased. The

design was to remain open to innovative ideas, make use of new manufacturing

The Design Proposal

27

methods and alternative materials as long as they add value to the product

without added cost and major complications.

3.3 Formalising The Design Brief

The design brief was formalised using the limited information given both

verbally in and writing by Design Mobel at the commencement of the project.

These design requirements were set out in a systematic manner so that those

presenting the brief could verify that the designer had the same goals for the end

product. The requirements were as follows: Design a bed adjustability

mechanism that:

• Must be a full working prototype by the end of 2001 and in production by

mid 2002 (Constraint)

• Must integrate into the frame of the latest bed range (Objective)

• Is simple and aesthetically pleasing to the eye (Goal)

• Price range approximately $250-$400 a side (Constraint)

• Not aimed purely for convalescing but for general home use in aiding

activities such as watching television, reading or feeding the baby

(Objective)

• Must be adjustable from within the bed by the user with minimum force

(Objective)

• Avoid the use of electricity in the bed (Goal)

• Must comply with the 330mm slat spacing system established for the

Circadian system (Constraint)

• In a double adjustable bed the two sides must have independent

adjustment (Constraint)

• Other

o Mattress design outside the scope of this project

o Ergonomics outside brief

o Need to establish the context of the product in the market

28

4 Approach to the Problem

As described earlier the project followed the Pahl & Beitz methodology for

systematic design, starting with the clarification of the task and continuing on

through to the detail design phase. This chapter gives a broad overview of the

steps that were taken in each stage of the design process. These steps will be

discussed in more detail in subsequent chapters.

Gantt charts were used throughout the project to establish the direction and time

goals required to complete tasks on time. The diagrams below summarise the

details of these charts to show the steps that were taken at each phase of the

design process (Table 4-1), and the timing involved for each (Figure 4-1).

Table 4-1 The design techniques used at each step of the design process

Clarifying the Task Conceptual Embodiment Detail Brief Brainstorm Load Distribution Value Engineering

Objective Tree Synectics Prototype Production Function Structure Generate Alternatives User Trial

Patent Analysis Morphological Chart Product Analysis Evaluate Alternatives

Adj. Activity Survey Bed Adj. User Trial

QFD PDS

Figure 4-1 A time based distribution of each of the design phases

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec20012000

Clarifying The Task

Conceptual

Embodiment

Detail

Approach to the Problem

29

4.1 Design Focus

There is little point developing a product for which there is no recognised need

or want. Accordingly the design should be approached with the focus of

fulfilling the needs of the consumer, and as a result achieving customer

satisfaction. However, there is the problem that the product being developed

may not be a perceived need by the customer while it still does not actually exist.

The desire is that the product is released and the customer realises its worth, and

the manufacturer will have then established a need. Whether it is a perceived

need or not the design should be developed so that it will meet the desires and

requirements that the user would have of such a product. Wherever possible

user feedback on the design and other relevant areas should be obtained to

determine this ‘voice’. This was done practically throughout the project through

the extensive use of questionnaires and user trials.

Throughout the project a systematic approach was applied:

• Gantt charts were used to manage the timeline of events and to establish

specific time goals.

• A design journal was used to record all thoughts, concepts, and

calculations. Any piece of work that was performed on paper was

recorded in the journal, making it easier to go back and find the

information required. Earlier conclusions could be located to speed up the

decision process, and important discoveries could be used to ensure the

same mistakes were not made again.

• All documentation was printed and sorted into folders logically for easy

access.

• At the end of each major task a summary of the work and results was

created. This helped to keep all the work up to date and meant that

nothing was overlooked.


30

Typically in a busy design office it is not possible to stand back from the design

and look at the approach being taken, as there are huge time pressures of

achieving results. In contrast, with this project there was the ability to stand

back, and to perform considerable research into the ideal methodology with

which to approach the design problem. Using the techniques discovered,

documents were prepared to help the flow of ideas and information at each stage

of the design process. After considering all the information, the Pahl and Beitz

methodology described in the background section was the process model that

was applied to the project. Design techniques were also used in conjunction with

the model to aid the development of ideas and information in each of the design

phases. The research was both beneficial in producing a methodology to be

followed and locating other aids to help in the process, but also in instilling a

design ethic that can be carried into future design projects.

The project also had to be undertaken with an environmental focus. Design

Mobel is accredited with ISO 14001, which requires that the product be designed

with great consideration on the affect the entire design cycle will have on the

environment. This covers everything from the production and its working life,

through to the retiring and recycling of the product. Consequently there has to

be a focus on the materials and the manufacturing methods used.

4.2 Clarifying the Task

Clarifying the task phase involved collecting all the information on the

requirements and constraints that were related to the product. To gain a firm

grasp on what the problem was really about required considerable research. This

started with the clarification and amplification of the design brief and extended

to background research into products already on the market, those already

patented, and into the ergonomics of adjustable beds. The voice of the customer

was used as a focus throughout the process and this was provided as part of the

task clarification with a questionnaire and user trial. Several design techniques


31

were also applied to help in the development of the PDS: the objectives were

determined using the objective tree technique, the functions were established

using function analysis, and the engineering characteristics were targeted using

Quality function deployment (QFD). All the information collected thus far was

compiled to create the preliminary PDS document. The conceptual design phase

and subsequent phases were based on this document and it was continually

updated as developments were made.

Throughout the clarification of the task phase a series of questions were asked to

assist the designer in thinking objectively about the problem and to continue

seeing the whole without getting carried away with the specifics.

The questions were as follows:

• What is the problem really about?

• What implications, wishes and expectations are involved?

• Do the specified constraints actually exist?

• What paths are open for development?

The clarification of the task phase took longer than expected because the design

brief was very broad. It was not until this document had been produced that the

design could proceed with confidence, with the knowledge that the product was

what Design Mobel truly desired.

4.3 Conceptual Design

The next stage of the design process was the conceptual design phase where

many concepts were developed and refined down to obtain the principle

solution. The plan was to use as many different design aids as possible to be able

to get the broadest range of suitable concepts. Brainstorming and synectics

sessions were performed with a group of people to develop some wild and

varied ideas for further investigation. Techniques such as objective trees,


32

function structures, and morphological charts were used to guide and structure

the thought processes while leaving room for creativity. The development of

these concepts took a little longer than planned but this process was critical due

to the emphasis given to the innovative nature of the design

The large list of concepts was reduced to a few suitable solutions using an

evaluation methodology. The design was broken down into four main sub-

systems: the frame, the adjusting mechanism, the method of actuation, and the

method of fastening the sub-assemblies together. The sub-system that affected

the other assemblies in the greatest manner was the method of actuation because

it influences almost every area of the design. A great deal of research was

required before a final decision was made on which method of actuation to

proceed with. Tentative decisions on the mechanism meant that the whole

system slid into the embodiment phase. The frame and fastenings had to be

moved into the next phase with assumptions of how the actuation would occur.

The design teetered between the two phases for some time, with new pieces of

information gathered, dead end designs discovered, and new ideas developed.

Once a final decision was made on the method of actuation the fuzzy concepts in

the other sub-assemblies could finally be clarified and developed further.

4.4 Embodiment Design

This phase involved clarifying and expanding the form design developed in the

conceptual phase and the concepts that had not been fully resolved were

elaborated until suitable decisions could be made. As the project progressed and

new knowledge was gained the evolution of the bed sub-assemblies was iterative

in nature because progress in one area would affect the design in another. As

stated earlier the final actuation method had not been confirmed until more

research into available techniques and the corresponding adjustment

mechanisms had been performed. Pneumatics was initially pursued as a suitable

actuation method but was later dropped for gas-struts, and then finally for


33

electric actuators. The adjustment mechanism also changed greatly during the

embodiment phase as improved techniques were developed and more

information on the rest of the system was clarified.

Detailed calculations were required to determine information such as the

dimensions, materials and velocities. The computer modelling was performed in

SolidWorks, the CAD software used at Design Mobel, making the transfer of

models simple and easy. A package called Dynamic Designer was used within

SolidWorks to test the kinematic properties of the models. Another SolidWorks

addin called Cosmos was used to perform Finite Element Analysis (FEA)

calculations on the parts to determine the stresses and strains induced by the

loads involved.

The concept was developed to a preliminary layout level so that a working

prototype could be produced in order to have a physical, tangible model to test

the theory of the design. This was also done so that all the unforeseen design

implications could be ironed out at this early stage before the definitive design

was developed. The prototype was used to perform a user trial to gather

information about the embodied bed design: their ability to use the bed, their

opinions of the system, and their perceptions of its overall comfort. Three

actuators were tried on the prototype to determine which was the best method to

use in the final design. The collected information was helpful in determining

which areas of the design needed to be changed and which areas were

satisfactory. At this stage the PDS was updated to cover the new data and

changes to the design. The major constraint of avoiding the use of electricity in

the bed was changed when it was discovered that the other possible actuators

were not viable and the only means to achieve the PSD satisfactorily was to

compromise in this area.


34

4.5 Detail Design

The work covered in this document finished with the review of the prototype

design and the changes and recommendations that were made as a result. The

prototype proved the concept would fulfil the problems set out in the PDS and as

a result the goal of the project had been reached. At the time that this was

written the level of development in many areas of the design was at the

beginning stages of the detail design phase and consequently the detail design

phase is outside the scope of this thesis. Following the writing of this thesis the

project will move completely into the detail design phase where the definitive

design will be developed for manufacturing processes so that it can be put into

production.

35

5 Determining the Design Requirements

This chapter describes the techniques and methods that were used to determine

the design requirements for the adjustable bed. This section essentially covers

the work that was performed at the beginning of the project, during the clarifying

the task phase.

5.1 Background Information

To establish the context of the project the following research studies were

executed.

Ergonomics

Research was undertaken into the ergonomics of adjustable beds with Dave

Tappin from South Pacific Ergonomics Ltd. Most of the relevant information was

gathered from documentation on the ergonomics of seating rather than from

information written specifically on sleep or lying down. This was because the

databases did not contain any papers on sleep or adjustable bed research and the

ergonomics of an adjustable bed are essentially that of a reclining seat. A list of

books relevant to this area of research is listed in the bibliography.

Analysis of Currently Available Products

One of the first steps that was taken in gathering information for the

requirements for the Design Mobel bed, was to establish the design context into

which the product was to be introduced. There are many adjustable beds

available around the world, with the majority of these beds originating in

Europe. A few of these beds are available in New Zealand and it is these

products that the Design Mobel adjustable bed will be competing with.

Two studies were performed to determine what customers would expect from

an adjustable bed, in regards to the performance, adjustment and features

Determining the Design Requirements

36

available. The studies were also used to discover what kind of mechanism and

sources of actuation have been used in the competitor’s products. One study

looked at the patents that had been filed in the adjustable bed area and the other

looked at the products that are currently being marketed. Both of these studies

were performed in much the same way, with the data that was collected analysed

using matrix analysis, to build up information regarding the features available in

these products and the advantages and disadvantages of each.

Patent Analysis

The patent analysis involved determining what intellectual property had been

filed in the area of adjustable beds, and what features and mechanisms this

covered. The search was performed through the Delphion Intellectual Property

Network website (Delphion 2001) where over 250 related patents were found. A

summary of the results are found in Appendix A. Many of these patents were

not relevant to the research area because they covered aspects other than the

mechanism for adjustability. 48 patents were found to have information

applicable to the project area and within these patents were a series of different

categories as shown in Table 5-1. Adjustable beds that alter the occupant’s

posture were the most significant group, with the other categories, such as height

adjustment, safety mechanisms, mattress supports, and motive units, in much

smaller numbers. The remainder of the analysis looked purely at the patents

covering the adjustment of posture.

The number of beds that were designed specifically for hospital use or for the

home environment (Table 5-2) was almost the same, with over half the adjustable

beds patented not indicating they were specific for either. The most significant

form of actuation for the home targeted beds (Table 5-3), was the use of electric

motors (48%), followed by inflatable bladders (17%), cylinders (13%), and

manual electric (9%). Looking at the mechanism behind this actuation (Table

5-4), the pivotal lever arm was the most significant with use in 65% of the beds.


37

The results also showed that 86% of these electrically actuated mechanisms used

pivotal lever arms.

Table 5-1 Different types of devices covered in the adjustable bed patents

Type of Adjustment No. %

Adjustable Bed 31 64.6

Height Adjustable 5 10.4

Size Adjustable 2 4.2

Angle Adjustment 2 4.2

Roll Adjustment 2 4.2

Motive Unit 2 4.2

Safety Device 1 2.1

Mattress Support 1 2.1

Sleep Conformability 1 2.1

Hardness Adjustability 1 2.1

Table 5-2 Proportions of the patents designed for the hospital and the home

Target use of Design % Not Stated 51.6 Hospital 25.8 Home 22.6

Table 5-3 Percentages of the different actuation methods used in the bed patents

Source of Actuation All (%) Home & Not Stated (%)

Electric Motors 45.2 47.8 Inflatable bladders 12.9 17.4 Cylinder 12.9 13.0 Manual Crank 9.7 4.3 Not Stated 6.5 0.0 Manual/Electric 6.5 8.7 Manual Move 3.2 4.3 Body Weight 3.2 4.3


38

Table 5-4 Percentages of the different adjustment mechanisms in the patents

Source of Actuation All (%) Home & Not Stated (%)

Electrical (%)

Pivotal Lever Arm 64.5 65.2 85.7 Inflation Of Bladder 12.9 17.4 14.3

Cylinder Movement 12.9 13.0 21.4

Pivotal Slide Mechanism 16.1 8.7 0.0

Screw & Nut 12.9 8.7 0.0

Torque Tube 9.7 8.7 21.4

Pulley And Wires 6.5 8.7 7.1

Hinge Movement 6.5 8.7 14.3

Gearbox/Worm Gear 6.5 4.3 0.0

Circular/Linear Gear 3.2 4.3 0.0

Scissor Mechanism 3.2 0.0 0.0

Gear Train/Clutch 3.2 0.0 7.1

One of the features that was present in 16% of the patents (Table 5-5) was the

ability to change the height the bed was off the ground. The analysis also

showed that this feature was not present in any of the home targeted beds. From

this data it was concluded that this would not be a necessary requirement and

would not be worth including in the Design Mobel bed design.

Table 5-5 Percentages of the bed patents with height adjustment

Height Adjustment All (%) Home & Not Stated (%)

Home (%)

No height adjustment 83.9 91.3 100.0 Total height adjustment 16.1 8.7 0.0

Table 5-6 shows that all but one of the beds had an adjustable back section. The

adjustment of the leg section was almost as significant with 87%, and the division

of the leg into an adjustable thigh section was also popular with 74% of the beds

featuring this adjustment. The option of adjustable head and foot sections was

not very popular with only three of the beds offering this. From this research it

was concluded that the basic requirement for the design would include back, leg

and thigh adjustment.


39

Table 5-6 Proportions of the patents providing adjustment at each of the body zones of the bed

Body Zone Adjustment All (%) Home & Not Stated (%) Home (%)

Back 96.8 100.0 100.0 Leg 87.1 87.0 85.7

Thigh 74.2 78.3 71.4 Head 6.5 4.3 14.3 Foot 6.5 4.3 14.3

There were additional options that were specific to a select number of models.

These features are listed in Table 5-7.

Table 5-7 Features of the patented adjustable beds

Feature Description

Add on kit A kit that can be easily assembled at home and installed on one’s bed in order to transform it into an adjustable one

Slide back As the bed is raised to a seated position the mattress support moves backwards to keep the person in the same position relative to any objects such as a bedside table

Anti jam A safety device is built in to stop parts of the body from being caught between the frames of the bed while moving

Butt depression A depression in the mattress section to accommodate the buttock when the bed is in a sitting position

Removable motor Motor is easily removed to allow for quick changeover

Power change The adjustment mechanism can switch easily between electric and manual power

Locking Mechanism The device uses a strap attached to a bell crank to activate a push/pull crank that locks the bed in position

Automatic knee break A cam is used to engage or disengage the knee adjustment with movement of the back section

Angle sensors Mercury sensors or rotary potentiometers are used to measure the angle of the bed

Vibrator Bed can vibrate for a massaging affect

The other interesting statistic to note was that 71% of the home targeted patents

for the adjustability mechanism had expired. Further research would be required

to determine the reasons behind this.


40

Product Analysis

The product analysis involved analysing the adjustable beds available in the

market place. A large number of product brochures had been gathered in

preparation for designing the adjustability mechanism. A total of 129 different

beds were analysed from 19 different companies. A complete summary of the

results is listed in Appendix B

The analysis of the adjustment (Table 5-8) provided by the products showed that

78% of them provided back adjustment, with 66% providing a head adjustment

option. For the leg, 95% provided adjustment but only 41% had bent leg options.

The results imply that the adjustment of the back and leg is a minimum

requirement, with the head and bent leg a possible inclusion in the design.

Telescopic head sections were only provided by two models, and 11% of the head

section’s mechanisms were linked to the movement of the back section.

The most common method of movement for the head section was manual (59%),

followed by electrical adjustment (37%). The adjustment of the back section was

split almost equally between manual (48%) and electric (46%). This was also

reflected in the leg adjustment with 56% manual and 42% electric. Gas cylinders

did not feature in the head adjustment and were only available in 7% of the back

and 3% of leg adjustments.

Only 4% of the beds gave the option of height adjustability. For the control

(Table 5-9), 82% of powered adjustable beds had cable remotes for adjustment,

8% had infrared remotes, and 9% used gas cylinder control. Table 5-10 shows the

different features that were available in the products.

The results from the matrix analysis gave valuable data on the amount of

adjustability required by the mechanism and the kind of features and control

expected by such a bed. The information also gave a good indication of the types

of mechanisms, materials, and features favoured by other manufacturers.


41

Table 5-8 The method and level of adjustment available in the products

% Yes % Answered

Adjustable 65.89 100.00

Telescopic 1.89 82.17

Linked 10.62 87.60

Manual Adjustable 59.21 58.91

Gas Cylinder 0.00 71.32

Head/Neck

Electric Adjustable 36.49 57.36


Manual Adjustable 48.00 77.52

Electric Adjustable 45.92 75.97 Back


Buttocks Fixed 41.09 100.00


Knee Separate 40.59 78.29


Manual 55.93 91.47

Electric 41.53 89.92

Leg


Table 5-9 Proportions of the different remote control adjustment methods

Remote Type %Yes % Answered

Cable Remote Control 82.09 51.94Infrared Remote Control 7.46 51.94

Cylinder Control 8.96 51.94

Table 5-10 Features available in the adjustable beds

Feature Description

Mains isolator Of the electrical beds 20% said they had mains isolation but the rest were unknown

Fits any bed frame 6% could fit any bed frame.

Bed box access 16% could lift the leg section right up to expose a storage area

Slide back 3% could slide as they raised to keep the person the same distance from the bed side objects

Centre belt 41% of beds had a centre belt to adjust the tension down the length of the bed

Emergency lowering Of the electrical systems, 18% stated they had an emergency lowering system


42

Feature Description Memory positions 21% of the electrical beds gave the option to record favourite positions

Power failure lock 7% of the models stated that on power failure their bed would not drop but lock in position

Removable motor 18% had motors that were easily removable

Load Distribution

For design purposes an indication of the loads that were to be expected along the

surface of the bed had to be determined. A study was performed by Design

Mobel to establish the load profiles of subjects based on different

anthropometrical constraints. Design Mobel purchased a device called Ergo

Check to perform the profiles. The device was basically a special blanket that

was laid on the bed to record the pressure readings created by the weight of a

subject lying on it. Screen shots from the Ergo Check computer software were

taken of each profile and with the help of Adobe PhotoShop the weight

distributed to each zone was calculated. The method was fairly accurate but a

small amount of the participant’s weight could not be accounted for. This was

because when the person sank into the mattress a slight sideways force was

produced which was not recorded by Ergo Check. The data from this study was

used to determine the maximum weight distribution on the bed’s surface and the

final results are shown in Table 5-11 and Figure 5-1.

Table 5-11 The mass on each bed zone and groups of zones under the worst load case

Bed Zone Zone Mass (kg) Multiple Zone Mass (kg)

A = Head 9.2

B = Back 44.8 60kg

C = Buttocks Fixed Fixed

D = Thigh 30.7

E = Knee 15.0

F = Foot 6.9

50kg


43

45kg 50kg

10kg

A

B C DE F

Figure 5-1 Worst case weight distribution on the head, back and leg sections

As the bed is raised from the flat position, more weight should move towards the

buttocks area, reducing the weight on the adjustable sections. The person is

essentially moving from a lying position to a sitting position so the weight

should be more concentrated in the fixed buttocks area. To verify this hypothesis

a study was performed with Ergo Check on the Dico adjustable bed used in the

adjustability user trial.

The readings were taken from 14 participants who were asked to lie on their side

and then on their back on both a flat and maximum configured bed. Figure 5-2

below shows an example of one of the results that was obtained from the

adjustability trial with the Ergo Check. The top box shows the weight

distribution of the subject lying on a flat bed with their head at the left hand end,

their legs on the right, and the large depression showing the buttocks area. The

image at the bottom shows the result of adjusting the bed to the maximum

configuration. Here the weight has moved from the extremities and has

increased the depression in the buttock’s zone

Since the study was very small no clear indication was found of the extent to

which the weight distribution would change when the bed was adjusted.

Nevertheless, the conclusion that can be drawn is that the weight is going to

reduce, rather than increase, from the outer zones as the sections are raised. This

is helpful information in the calculation of stresses for the mechanisms.


44

Although this is true, the shock loads created by a person jumping on the bed are

much more significant and the true test of the bed will be factoring these forces

into the design.

Figure 5-2 A sample screen shot of the Ergo Check software results

5.2 Customer Needs and Preferences

When Design Mobel presented the brief for the adjustability mechanism there

had been no studies performed into the opinions of the customer. Design Mobel

had suggested there was a need for an adjustable bed but had not determined

exactly what this need was. A survey and a user trial were performed to gather

the valuable information required to determine the product the potential

customer would desire.

Adjustability Activities Survey

A survey was undertaken to determine what activities people carried out in bed

and what kind of adjustment could be supplied to assist them in these activities.

The questionnaire (0) was designed with help from Design Mobel and was tested

for suitability with a pilot study on 16 participants. The survey was then sent out

in pairs, to 275 households from Design Mobel’s database of valuable customers,

so that partners could also fill out the form. To increase the number of returns,

surveys were sent with stamped self-addressed envelopes, and the opportunity

to go into the draw for a Design Mobel wall mirror on the return of the form.


45

Even so, only seventy-seven individual replies were received which may have

been the result of sending the survey out during the Christmas period.

The complete results can be found in Appendix D. The returns suggested that

females were slightly more interested in responding (Table 5-12) and most of the

respondents were between the ages of 30-40 years old (Table 5-13).

Table 5-12 Number and sex of the adjustable activity survey respondents

Total Number 82

Male 29

Female 46

Not stated 7

Table 5-13 Age distribution of the respondents to the adjustable activity survey

No. Responded Age 75

Avg Age 37.8 ±10.4

Max Age 60

Min Age 17

Avg Male 39.3 ±11.12

Avg Female 36.7 ± 9.91

The first question in the survey involved asking the subjects what activities they

like doing in bed (besides sleeping and the other obvious one). Each activity was

rated on how much they enjoyed doing the activity in bed, how frequently they

did it, and how easy it was to carry out on a scale of 1-5 (Table 5-14). The most

popular activity was reading with an average pleasure rating of 4.22, followed by

watching television with 3.57, and phoning 3.49. This activity also had the

highest rating of ease at 3.50, with phoning and television watching following

closely behind again. A summary of the activities and the general response to

performing them is listed in Table 5-15.


46

Table 5-14 Pleasure, frequency and ease of performing the activities in bed

Activity Question Rating Std Dev No. Respond % Respond

Like 4.22 0.95 76 92.7

Freq 3.49 1.17 76 92.7 Read

Ease 3.50 1.01 74 90.2

Like 2.21 1.18 57 69.5

Freq 2.04 1.13 58 70.7 Work

Ease 2.42 1.32 48 58.5

Like 2.32 1.73 19 23.2

Freq 1.92 1.55 26 31.7 Feed Baby

Ease 2.35 1.54 17 20.7

Like 2.41 1.70 63 76.8

Freq 2.19 1.02 67 81.7 Sick

Ease 3.84 1.14 65 79.3

Like 1.92 1.16 36 43.9

Freq 1.67 1.06 46 56.1 Computer

Ease 2.50 1.25 30 36.6

Like 3.49 1.18 69 84.1

Freq 3.03 1.13 73 89.0 Phone

Ease 3.95 1.01 70 85.4

Like 2.42 1.15 53 64.6

Freq 2.07 1.11 58 70.7 Write

Ease 2.40 1.11 52 63.4

Like 2.51 1.30 59 72.0

Freq 2.35 1.11 63 76.8 Eat

Ease 2.74 1.18 58 70.7

Like 3.57 1.35 61 74.4

Freq 2.77 1.48 66 80.5 Television

Ease 3.40 1.20 60 73.2


47

Table 5-15 Summary of the participants opinions of performing each of the activities

Activity Opinion

Work Most people do not like to work in bed. There is a possibility that by increasing the ease of the activity more people would try to work from bed.

Feed Baby Obviously this is an activity only performed by a small group of people. Those who do feed babies do not appear to do it very often in bed and this may be due to the lack of ease. There could be possibility for improvement here.

Sick

Most people appear to think that the bed is suitably comfortable when stuck in bed sick. There is the possibility that if adjustment was available it would make things more comfortable but it is an unperceived need at this time for most people.

Computer Not many people appear to have laptops that they can use in bed and again most people do not like to use them for the same reasons as doing work in bed.

Phone

Most people find that they do speak on the phone in bed relatively often but do not appear to find it that difficult. It was suggested that the main problem with speaking on the phone is the room design and position of the phone rather than the bed positioning.

Write The difficulty in writing in bed is having a supportive surface in a suitable position. Writing while sitting in a normal bed is very and this is reflected in the number of people who actually try and the low rating in the ease of use.

Eat

Breakfast in bed during the weekend appears to be an activity that a number of people like to partake in but many do not like crumbs in their bed or the possibility of spilling food or drink through the bed. Being able to sit up properly will help the process but supporting the food is still an issue. This is an activity that could be aided with some sort of accessory tray/table that can be folded out.

Television

Participants were split in their views over watching television in bed. A number felt that a television was not necessary in the bedroom or did not actually have one in their bedroom. But the majority liked to watch television in bed and do so with moderate ease. Many also suggested that this activity could be made more comfortable by being able to raise the bed into a sitting position.

85% said they prop themselves up in bed (Table 5-16) and all but one person said

they use pillows to do so. A satisfaction rating of 3.11 was given for this method

(Table 5-17) suggesting that people find propping themselves up with pillows

adequate but not ideal.

When the participants were asked if they would like to have independent sides

for adjustment in a double bed (Table 5-18), the outcome was very much in

favour for complete independence, with a rating of 4.48.


48

Table 5-16 Respondents who prop themselves up in bed and for what activities

No. % No. Respond % Respond

Prop up in bed 70 85.37 76 92.68

Read 50 60.98 50 60.98

Television 27 32.93 27 32.93

Eat 18 21.95 18 21.95

Phone 14 17.07 14 17.07

Write 9 10.98 9 10.98

Study 6 7.32 6 7.32

Work 4 4.88 4 4.88

Computer 4 4.88 4 4.88

Drink 3 3.66 3 3.66

Activities to

Prop

Pillow 69 84.15 69 84.15

Use Headboard to Prop 0 0.00 69 84.15

Table 5-17 Respondents satisfaction of propping themselves up in bed

Avg Rating Std Dev No. Respond % Respond

Satisfaction of propping 3.11 1.01 69 84.1

Table 5-18 Respondents desire for independently adjustable halves of the bed

Avg Rating Std Dev No. Respond % Respond

Desire for Independence 4.48 0.99 75 91.5

When presented with a series of adjustment options (Table 5-19), most people

just wanted to be able to sit up in bed with as little leg movement as possible.

People appeared to be weary of the possibilities of using an adjustable bed

because they are unfamiliar with such a concept. It was proven with later trials

that the response to using the bed was much more positive once respondents

were actually able to try the bed.

The completed questionnaires were very helpful in determining some of the

perceptions of the end user and what they would like in an adjustable bed

system. The information gathered was collated and added to the pool of data in

the PDS document.


49

Table 5-19 Level of adjustability desired by the participants

Position Rating Std Dev % Respond

3.59 1.51 89.0

3.07 1.10 89.0

3.02 1.15 89.0

2.98 1.37 89.0

2.33 1.48 89.0

Bed Adjustability User Trial

Up until this point no data involving the user’s perception of properties such as

the speeds, comfort, and desired angles of the mechanisms had been tested. Such

data would be essential for the QFD study, which was still to be performed. A

user trial was set up to obtain this information with the focus on the activities

people carry out in bed (excluding sleeping and the other obvious one!) and how

the ability to perform these activities could be improved.

The trial involved testing 32 individuals (Table 5-22) at the Design Mobel factory

in Tauranga from Thursday 15th - Fri 23rd Feb, with each test taking


50

approximately 30 minutes per subject. The subjects were selected to fit the

desired target customer between the ages of 25-40; who fitted the required

anthropometrical zones based on sex, height and weight. (Table 5-21, Table

5-22). The trial activities were performed on a Dico 498 adjustable bed that had

been purchased from Germany. The Dico bed provided a suitable level of

adjustability to test the appropriateness of an adjustable back and leg sections.

The bed was set up in the design office, as seen in Figure 5-3, with made up as

close tot hat as a standard bed.

Table 5-20 Total number of males and females in the user trial

Total 32

Male 22

Female 10

Table 5-21 Distribution of female participants based on height and weight

Group Quantity Height (mm) Weight (kg) A 1 42-60 D 0 60-78 G 0

1480-1580 78-96

B 2 42-60 E 2 60-78 H 0

1580-1680 78-96

C 2 42-60 F 2 60-78 I 1

1680-1780 78-96

Table 5-22 Distribution of male participants based on height and weight

Group Quantity Height (mm) Weight (kg) D 5 55-73

G 1 73-91

J 0

1610-1710

91-109

E 3 55-73

H 5 73-91

K 3

1710-1810

91-109

F 1 55-73

I 2 73-91

L 2

1810-1910

91-109


51

Figure 5-3 Photo showing a participant being tested in the adjustability user trial

The subjects were asked to perform six activities in the bed in the following

order: reading, watching television, writing, using a phone, using a computer

and eating. An indication of general comfort was all that was possible because of

the time constraints of the study. Each activity was performed on the bed in the

flat configuration, to represent a standard bed, and the subject was asked to rate

the comfort. This same activity was then performed with the bed adjusted to the

participants most desired position and again the comfort rating (out of 10) was

taken and the angle of the bed recorded.

The results (Table 5-23) clearly showed that by adjusting the bed, the ease and

comfort was greatly increased. Most of the activities were increased between 2-4

grades with the adjustment of the bed. Activities requiring a very upright

position, such as using a computer, writing, and eating, needed large amounts of

back and neck support with back angles as great as 60 degrees. The study

showed that the desired angles would have to be as great as 80 degrees to satisfy

the 16% of users who wanted a higher back angle. The adjustment of the leg was

much more varied from activity to activity and dependent on the individual’s

preferences.


52

Table 5-23 Ratings and angles given by the participants for each activity

Flat Angled Difference

Activity Rating Std Dev Rating Std

Dev Angle

Leg Angle Back

Avg Diff

Std Dev t-Test

Read 5.4 2.14 8.5 1.17 4.7 42.2 3.0 2.24 1.28x10-8

Television 5.3 1.95 8.7 0.97 13.9 36.4 3.4 1.77 4.69x10-12

Work 4.4 2.25 7.9 1.01 15.8 51.1 3.5 2.29 8.7x10-10

Phone 5.5 2.32 8.0 1.28 9.1 24.8 2.5 2.12 2.07x10-7

Computer 4.0 2.61 7.9 1.19 12.5 53.0 3.9 2.61 3.39x10-9

Eat 4.5 2.30 6.8 1.54 4.7 59.2 2.4 2.83 4.33x10-5

The trial was completed with a post-test questionnaire that asked a number of

questions on many aspects of the bed including the performance, ease of use, and

the control device. As well as a series of quantitative results (Table 5-24), many

helpful qualitative results were recorded from the subject’s comments. It was

interesting to note that most of the participants were very impressed by the Dico

system once they had used the bed and they were quite satisfied by the

performance it delivered. If the performance of this model could be beaten or at

least matched, the final design would be more than satisfactory.

Table 5-24 Participants average ratings from the post questionnaire

Question Avg Rating Std Dev

Control device ease of use 8.08 1.59

Control device understanding 8.59 1.41

Force required to operate control 8.81 1.35

Each of reaching the control 6.52 2.11

Ease of obtaining desired angles 8.39 1.42

Speed 7.86 1.48

Smoothness 9.03 1.13

Noise 9.24 1.18

How at ease they felt using the bed 9.00 0.85

Safety 8.38 1.78

Robustness 8.48 1.40

Firmness 8.59 1.37

Appearance 7.26 2.19


53

5.3 Design Techniques

Using the information collected from the background research and the customer

feedback, a series of design methods were used to define the direction of the

project: objective trees, function analysis, QFD, and the creation of the PDS.

Objectives Tree

The list of requirements that had been collected and developed up until this point

were ordered into groups of similar function and attributes. The objective tree

method detailed in Cross (1994), gave structure to the requirements through the

production of a hierarchical tree of these objectives. The production of the tree

was used to determine which were the most important attributes and how they

might interact and affect each other. The process also made it quite clear where

there were gaps in the information. Having identified these gaps they were

further evaluated so the tree could be studied and filled with the appropriate

objectives as shown in the final as shown in Figure 5-5.

Function Analysis

With the objectives detailed, the functions required by the adjustable bed were

analysed using the method described in Cross (1994). The adjustable bed had an

obvious main function, shown in Figure 5-4; where the user determines that they

need to adjust the sleep surface and they use the control to move it to the desired

position.

→ User performs action to adjust bed section(s)

→ Particular

section(s) of the bed adjusts

→ User reaches

desired position

User: • Uncomfortable • Wants to move into

position suitable for a certain activity

• Wants to lie down

Figure 5-4 General function structure for the adjustability mechanism


54

Figu

re 5

-5

The f

inal

obj

ectiv

es tr

ee d

evelo

ped

usin

g th

e obj

ectiv

e tre

e met

hod

Adjustability

Mechanism

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grat

ion

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sive

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tegr

atio

nTw

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n w

ell

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imum

of p

arts

in

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tive

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Adjustability

Mechanism

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volv

ed

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gy

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(Sub

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mov

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fli

ckin

g up


55

This function can be further expanded to show the sub-functions:

• The user’s motivation

• How the actuator stores the power to make the movements

• The input the user initiates to activate the actuator

• The actual mechanism to move the bed sections

Functions could not be developed in detail until the actuation method had been

developed. Once a list of possible methods of actuation had been established the

function structures corresponding to these were created in detail and are shown

in Appendix F. The function structure was very helpful in clarifying the

processes that were required by the design so that features could be developed to

meet these requirements. The method was also useful in showing the break-up

of the system into subassemblies and that similar functions were shared by

different structures. This meant that even though the solution to one of the

structures may not be defined, progress could be continued in another area and it

would still be guaranteed to be relevant to the other subassemblies.

Quality Function Deployment (QFD)

A QFD study was executed using the data collected from the survey, trial, and

background research. The process that was taken followed the procedures set

out in Cross (1994) and is shown in Appendix G with the final, the QFD chart

shown in Figure 5-6. The large chart may appear somewhat overwhelming but is

actually quite simple to follow and very useful to apply.

On the left hand side of the chart are the customer requirements and along the

top the engineering characteristics required to meet these. On the right hand side

the customer requirements are given a level of importance and for each of the

different beds a rating out of ten is given for that attribute. The study used a

standard non-adjustable bed as the benchmark and the Dico bed as the product

to be compared against. Taking the values of the other beds and the relative


56

importance, a list of targets (far right of the table) was produced that the final

design should meet to satisfy the customer.

Figure 5-6 QFD Chart 19/3/01

At the bottom of the table the engineering characteristics are measured for the

standard and Dico beds. Again a set of design requirements was created, this

time in regards to the engineering characteristics of the final design. At the top of

the table is the triangular roof that indicates the interactions between the different


57

engineering characteristics. Just below the roof are a series of arrows and circles:

an upwards arrow indicates that the greater the engineering characteristics the

better, a downwards arrow being the opposite, with a circle suggesting neither

up or down is necessarily better. Within the roof, a cross indicates that the

interaction is negative, a hollow circle indicates a positive outcome, and a solid

circle indicates a strong positive outcome.

The outcome from the study was a comprehensive set of engineering design

targets, and operation and performance goals that were included in the PDS

document, which ensured that the design could now progress with definite and

realistic objectives to achieve.

Product Design Specification (PDS)

Collating all the information that had been gathered in this phase allowed a more

complete but tentative PDS to be produced. Throughout the clarification of the

task period the list of requirements was expanded so that it was clear exactly

what had to be designed. It was not until the QFD had been completed that a

fully developed PDS was created and the design moved into the conceptual

phase. Throughout the project this document was refined and developed to

cover the new discoveries that were made as well as the necessary compromises

to allow for unrealistic constraints. The final PDS document is found in Table

H-1.

58

6 Developing the Concepts

The following chapter discusses the steps that were taken to generate a series of

concepts and to evaluate them down to a principle solution.

6.1 Brainstorming / Synectics Session

During the initial stages of the design process several brainstorming sessions

were held to begin the construction of the concept for an adjustable bed. The

sessions were designed to create a flow of ideas and flesh out the potential needs

and requirements of such a system.

Initial Session

In mid December 2000 a meeting was held for all those involved in the

development of the Circadian design. The members involved in this meeting

were experts from a variety of fields outside of Design Mobel, from the

production and design of the plastic parts to the development of the aluminium

side rails. The session was performed using the method suggested by Cross

(1994) where each member of the group is asked to spend a few minutes in

silence writing the first ideas that enter their head in response to the initial

problem statement. The next step is to have members take turns at reading out

one idea from their list with the important rule for no criticism. Each group

member should try to respond to every other person’s ideas, using it as stimulus

for other ideas, or to combine with their own ideas.

The adjustability activities questionnaire (section 5.2) showed that many people

were interested in reading in bed but thought it could be made more comfortable.

In response the initial problem statement used in the brainstorming sessions was,

“How can we make reading in bed easier?’ This lead to many off the topic

responses directed at accessories rather than modification to the bed itself. Once

the conversation was directed more towards how adjustability could be used to

Developing the Concepts

59

aid reading, more appropriate ideas were suggested. As the time went on, the

thinking was switched to “What kind of power could be used to move the bed?”

and “What kind of mechanisms could be used?”

Below is a summary of some of the ideas that were generated in terms of

adjustment and accessories.

Adjustment: • Headrest only • Counterweights

• Pneumatic bladder • Slight knee movement to prevent slippage

• Cam adjustment of sleep contour • After time bed returns to flat position

• Temperature controlled Gel • Personal movement Accessories: • Built in light • Foot stops

• Fold out armrests • Lumbar support Once the ideas dried up the session shifted toward using synectic analogies to

create some more suitable ideas. A few suggestions were made during the

session but the method did not appear to work as well as planned. The absence

of creative analogies may have been a result of the lack of interest in the group,

potentially due to the length of time already spent in the meeting. The

unsatisfactory result may have also been due to the more tangible brainstorming

solutions blocking the thinking processes, or even an unclear explanation of the

synectics idea.

Analogies: • Moss • Water: Floating in water

• Sand: Pile up sand to form a pillow • Ligament and muscles moving a skeleton Analogous Devices: • Lazyboy • Deck chair

• Dentist chair • Car seats

• Airplane seat • Bean bags

• Dynamic chair


60

The response to the array of ideas was largely constructive and positive, even

toward some of the more unconventional concepts. This in turn led to

participants shedding their intellectual inhibitions and allowing some more

abstract and creative ideas to surface.

University Session

The second brainstorming session was performed in the mechanical engineering

department in mid January where many of the postgraduate students, technical

staff and lecturers were invited to participate. The designer had developed a list

of concepts but the number of ideas had been exhausted, therefore it was

beneficial to use the group as a bouncing board for ideas and as a source of

potential solutions. The purpose of the session was to produce as many

mechanisms as possible to perform the bed adjustment.

The proposed method:

• Each person has a page with four columns.

• They take two minutes to write down as many ideas in column one.

• Take a two minute break, and then finish column one entries (30 secs).

• The ideas are read in turn, as others cross of duplicate entries from their lists

and write new ideas under column two.

• When the group has finished, the process is repeated, this time reading

column two entries and writing down any new ideas under column three.

• The process is repeated with a fourth column until all the ideas are exhausted.

The session was not as successful as was hoped with only five people turning up

and the amount of time available was limited. The planned brainstorming

technique also broke down into general discussion, however in the end this was

not necessarily unhelpful with many ideas being produced.


61

Below is a summary of some of the ideas that were generated during this session:

• Pneumatic bladder

• Mechanical Pivot Lever Powered by ram action

• Temp controlled Fluid/Solid

• Body weight Activated by sensor or lock

Requires something to push against? Car seats, or lazy boys work well but they have armrests

• Pneumatic cylinders Shift air from big to small cylinder

Body weight produces the compression of the air

• Electric People may feel most comfortable operating and using electric devices

Problems of electromagnetic fields in bed

6.2 Searching for Working Principles

The next stage was to amalgamate all the ideas that had been developed in the

brainstorming sessions and in personal work. The objective was to display all of

the possibilities for each sub-assembly of the system so to provide an overall

scope of the concepts and to also have them laid out together to aid in further

concept development. The ideas were broken into several categories;

mechanisms, adjustability, power, and operations shown below.

Mechanisms • Manual levers to move the bed sections

(lazy boy) • Screw drive mechanism

• Button pressed to allow body weight to adjust the sections (car seat or airplane seat)

• Scissors mechanism

• A dynamic device that adjusts under personal movements (dynamic chair)

• Pulleys and wires mechanism

• Manually adjustable bed (deck chair) • Circular/linear gear mechanism • Powered pivoting sections (most current

adjustable beds) • Telescopic mechanism

Adjustability • Head/back section only: Pivoted at top Pivoted at bottom

• Cams that can be rotated to give unadjusted contour

• Adjustable headboard that can fold away

• Adjustable frame Head Femoral


62

Back Tibial Fixed buttocks

Power • Electric motor • Counter weights

• Pneumatic cylinders • Springs

• Pneumatic bladder • Gravity

• Personal weight • Manual Operations Remote control:

• Cable or infrared • Memory positions

• Reset function • Sleep return Accessories:

• Foot stops • Arm rests

• Built in lamps • Lumbar support

• Massage system • A temperature controlled gel

• Slide back • Locks on power failure

6.3 Generating Alternatives

The morphological method listed in Cross (1994) was used to produce a series of

new concepts that build on the features that had already been developed. All the

essential features for the product were listed in a table with all the possible

solutions to them. By taking different combinations of the feature variations new

concepts were developed that may have otherwise been overlooked. Many of the

concepts that were developed were redundant yet there was the odd unexpected

variation that was suitable. The approach that was taken is shown in Appendix I.

One step taken in the process is the development of a table containing all the

possible means of achieving the required features and functions (Table 6-1).

From this list a multitude of various configurations can be drawn out

representing new concepts to the solution. For example, a proposed system may

have an adjustable head, non-parallel bent legs, pivotal lever arm mechanism,

compressed air actuation, full assembly, and no accessories. The concepts were

broken up into groups based on the form of actuation and mechanism used as


63

shown in Table 6-2. The outcome from the process was Table I-2 that lists all the

possible concepts generated from the method within these groups.

Table 6-1 The possible means to achieve each of the features and functions

Cam

s

Link

ages

Scis

sors

Scre

w D

rive

Pulle

ys/

Wir

es

Man

ual

Man

ual

mov

e

Dyn

amic

Air

Bl

adde

r

Hea

d /B

ack

Leg

Bent

NP

Pneu

mat

ics

Com

p A

ir

All

Asm

Slid

e ba

ck

Back

Leg

Bent

P

Pivo

t Lev

er

Arm

Pers

onal

W

eigh

t

Som

e A

sm

Fold

away

ar

mre

sts

Hea

d

Leg

Stra

ight

Cir

cula

r /l

inea

r gea

r

Elec

tric

Sepa

rate

1/3

2/

3 fr

ame

Built

in

lam

ps

Mea

ns

Non

e

Non

e

Non

e

Non

e

Full

Fram

e

Non

e

Asm

= A

ssem

bly

Feat

ure

Top

Adj

.

Leg

Adj

.

Mec

hani

sm

Act

uatio

n

Inte

grat

ion

Acc

esso

ries

Not

es:


64

Table 6-2 Summary of the concept groups generated in the morphological matrix

0 Benchmark beds

1 Air actuated

2 Cam electric

3 Cam manual

4 Linkage manual

5 Scissor manual

6 Screw electric

7 Pulleys/wire electric

8 Pulley/wire manual

9 Circular/linear gear electrical

10 Dynamic Personal Weight

11 Manual

12 Pivotal lever arm Electric

13 Pneumatic compressed air

6.4 Evaluating Alternatives

Once the concepts had been developed it was imperative to decide which were of

value to develop further. This can simply be done in an arbitrary way, by just

looking at a concept and deciding which is most appealing. Alternatively and

preferably this can be done in a quantifiable way, which adds confidence in

choosing the concept that is significantly better the others. The weighted

objectives technique described in Cross (1994) was used to compare the utility

values of the alternative design proposals. The different concepts were rated on

the basis of performance against differentially weighted objectives. A summary

of the weighted objectives process using the concepts from the morphological

matrix technique is shown in Appendix J.

The outcome from the evaluation technique is shown in Table 6-3, which ranks

the sub-concept’s utility values within its general actuation and mechanism

groups. The top concept from each group is highlighted with the pneumatic

system rating highest (797), the dynamic system second (770) and the electrical

pivotal arm system third (741). Therefore the principle solution at this point was

concept 13.6, which consisted of back and head adjustment, bent non-parallel leg


65

adjustments, pneumatic mechanism operating with compressed air with full

assembly and a slide back mechanism.

Table 6-3 A ranked summary of the utility values assigned to each concept

Group Model 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

4 Manual Linkages 527 516 549 538 525 571 560 547 3 Manual Cam 557 546 579 568 556 601 590 578

5 Scissor Manual 563 552 585 574 588 607 596 610

7 Manual Wire/Pulley 576 566 598 588 602 620 610 624

11 Manual 611 600 633 622 603 655 644 625

9 Elec Circ/Lin gear 607 596 629 618 639 651 640 661

6 Elec Screw 627 623 649 645 653 671 667 675

1 Air Bladder 648 638 670 660 654 692 682 676

2 Electric Cam 665 654 687 676 663 709 698 685

8 Electric Wire/Pulley 668 658 690 680 694 712 702 716

12 Pivot Arm Elec 697 686 719 708 695 741 730 717

10 Dynamic 726 715 748 737 738 770 759 760

13 Pneumatic 753 742 775 764 752 797 786 774

Establishing Degree of Adjustability

In response to the level of adjustability desired by the end user the system was

broken into a top and a bottom half with a series of options available (as seen in

Figure 6-1). The top half had three suitable options; (i) an adjustable head only,

(ii) adjustable back only or (iii) a combination of both head and back adjustment.

The bottom half also had three options; (i) the leg can be a single straight section,

or (ii) bent in a parallel or (iii) non-parallel manner.

Top Half Bottom Half (i) (i)

(ii) (ii)

(iii) (iii)

Figure 6-1 Top and bottom half adjustment options


66

Based on the information that was received from the different surveys and

adjustability user trials it was decided to make the top half back adjustable only

(top half option (i)) and the legs non-parallel bent (bottom option (iii)) as in

Figure 6-2. However as the embodiment design proceeded it was found that it

was not possible to obtain the angles desired without breaking the top half into a

back and head section and therefore the final design was modified as shown in

Figure 6-3 below.

Max 80 0 Max 30 0

Figure 6-2 The level of adjustability initially pursued

Max 60 0 Max 30 0

Max 30 0

Figure 6-3 The final breakdown of the adjustability

67

7 Embodiment of the Design

The following chapter describes in detail the major steps that were taken in the

embodiment design of the adjustable bed. During this phase the bed design was

divided up into several sub-assemblies: the frame, the back mechanism, the leg

mechanism, the adjustable rails, the actuation, and the method of mounting. This

section shows the progression of each of the subassemblies to the point where

they were developed for the prototype.

7.1 Definition of the Bed Subassemblies

The bed is of the flexible slat bed type, this means that the sleeping surface that

supports the mattress is produced by a series of slats. These slats are held in

place at each end by a shoe that is fixed into the bed frame as shown in Figure

7-1.

Shoe

Slat

Bed Frame

Detail View

Elevation

Figure 7-1 The arrangement of the slats and shoes in the bed frame

The bed frame shown below (Figure 7-2) consists of four side rails: two plain end

rails (tie rails) and two side rails with grooves for mounting the slat shoes. The

rails, shown in detail in Figure 7-3, are made from aluminium extrusion and are

joined at the four corners by plastic brackets. The necessary modifications were

made to the Circadian bed frame so that it can cradle the adjustable frame.

Embodiment of the Design

68

Figure 7-2 The Circadian bed frame that cradles the adjustability mechanism

Figure 7-3 Elevations of the side rail and end rail

The adjustable frame sits inside the bed frame and is made up of moveable

sections, which rotate up and down to give the desired contour of the sleeping

surface. The other purpose of the adjustable frame is to hold the slat shoes in

place. One of the major constraints of the Circadian system are the six 330mm

slat zones that control the articulation points of the adjustable frame as shown in

Figure 7-4.

Lower Leg Leg Thigh Buttocks Back Head

1980mm

330mm

Lower Half Upper Half

Figure 7-4 The break up of the bed length into 330mm zones


69

The back mechanism is the subassembly that performs the adjustment of the top

half of the bed including the back and head sections. Similarly the leg

mechanism is the subassembly that performs the movement of the lower half of

the adjustable frame. The method of actuation delivers the power to move these

mechanisms and has significant control over their final form and design. The

method of mounting relates to how each of the subassemblies comes to together

to mount on to the bed frame and is largely dictated by the design of the other

subassemblies.

7.2 The Adjustability Mechanism

This section looks at the various features of the adjustability mechanisms. The

items that are common to adjustability of both the leg and back sections are

considered first while their individual mechanisms are described in more detail

in sections 7.5 and 7.6.

Roller Mechanism

The first concept that was evaluated fully was a mechanism that operated using

pivoting arms to push the adjustable sections of the frame up. The strut pivots at

one end and moves freely at the other so that when it is rotated, the movement of

the free end causes the adjustable section to rise or fall. A roller was introduced

to the concept to reduce the friction that would be created if the two surfaces

rubbed against each other. There are many possibilities for the positioning of the

roller and the pivoting point within the mechanism layout. After considering

many factors such as the positioning of the actuators and interferences it was

decided that the strut would pivot from the bed frame with the roller starting

close to the head end and moving towards the buttocks to produce the lifting

motion (Figure 7-5).


70

Figure 7-5 The final arrangement of the roller concept

The purpose of the strut is to lift the adjustable section by rotating about the

pivot point under the power from the actuator. The length and size of the strut is

dependent on geometry and layout of the mechanism, the size of the frame side

rail, the method and position of the actuator, and the forces involved. Maximum

torque is produced from the actuator when the force is perpendicular to the

centre of rotation which can be achieved by adding a bend to the strut. Many

methods of mounting the roller to the strut were conceptualised and they were

all dependent on the form of the strut. The two most suitable concepts involved

producing them from a flat sheet or extruded metal strut (Figure 7-6) but both

had manufacturing problems that needed to be resolved.

(i) Flat Sheet (ii) Extrusion

Figure 7-6 Strut arrangements (i) flat sheet or (ii) extrusion

To produce the lifting motion on the adjustable rail, the wheel has to be free to

roll up and down on some sort of track. Many ideas were suggested but the most

suitable concept involved running the roller on the bottom of the adjustable rail


71

between a set of guides to keep it inline and the sidewalls of the rail were

increased to hide the roller as in Figure 7-7.

Figure 7-7 Roller wheel running on the underside of the adjustable rail

Slide Back

Slide back describes the concept of maintaining the subject’s body position

relative to a fixed point e.g. the bedside table or the wall, as the bed is adjusted

upwards. The mechanism slides back as the back section rises up to compensate

for the motion of the bed. A carriage concept (Figure 7-8) was conceptualised

that achieves this motion but it was found to be very complex as the whole of the

adjustable frame and mechanisms would have to move on this carriage. It was

also discovered soon after the idea was developed that the idea had already been

patented as seen in Figure 7-9. The slide back system was discarded as it was too

complicated and therefore would compromise the PDS desire for a simple and

inexpensive system.


72

Figure 7-8 The motion of the slide back carriage system

Figure 7-9 Slide back patent (WO9730614A1)

Adjustable Frame Form

The adjustable frame has to be strong and rigid enough to lift a body and be

capable of holding the slats in position to do so. The Circadian frame has

grooves along the length of its side rails to hold the shoes that maintain the slats

in place. These have to be mimicked in the adjustable rails and have to be at the

same height so that the slats sit inline with the rest of the slats along the length of

the bed. The only suitable positioning for the groove in the adjustable rail is so it

sits inline with the bed frame grove as shown in Figure 7-10. In keeping with the

styling of the frame side rails the adjustable rails are made from aluminium

extrusion.

Back Section


73

Figure 7-10 Positioning of the adjustable rail groove so that the slats sit inline along

the length of the bed

The adjustable side rails have to be joined to a cross rail to give a rigid, strong,

independently moveable section. Only one cross bar per section is required and

is best positioned at the end furthest from the point that the adjustable rail is

mounted to the side wall, as shown in Figure 7-11.

HeadBackThigh ButtocksLeg

Crossbar Pivot Point Figure 7-11 The adjustable frame showing the pivot points and cross bars

To avoid the complications and cost of developing a series of brackets to hold the

adjustable frame together it was decided to weld the frame together. Since the

frame will be made from aluminium, welding the frame together is a suitable

option and produces a pleasant style. The most suitable concept (Figure 7-12)

was to weld a standard aluminium extrusion to the inside of the parallel

adjustable rails, keeping the depth of the frame low and removing the need for

extra plugs to fill the ends of the cross bars.

There were major decisions to be made on whether to include the buttocks

section in the adjustable frame or not. The assembly will look tidy and uniform

along the length if the buttocks section is included but will be greatly simplified

when removed. The buttocks section was removed from the adjustable frame

helping divide the top and bottom halves of the mechanism as well as removing


74

the need for a special hinge to perform the articulation between both the back

and thigh sections with the buttocks. The disadvantage though is that when the

buttocks section is mounted on the bed frame, two different sized slats are now

required (Figure 7-13).

Figure 7-12 One crossbar is welded to the inside of the parallel adjustable rails at the

end furthest from the mounting end

Figure 7-13 Top view of frame showing the buttocks section mounted in the bed frame

and the two sizes of slats

A frame that would cradle the mechanisms and aid in the ease of assembly of the

system was considered as seen in Figure 7-14. The assembly is simplified with

only a few fasteners required but the concept was discarded, as it would add

weight, extra parts, and be unattractive.


75

Figure 7-14 The adjustable frames being assembled with a cradle frame

The total length of the bed was constrained at 2050mm leaving 70mm for hinges

and movement clearance after removing the 1980mm for the slatted zones. When

the slat zones were modelled in SolidWorks it was discovered that only a 35-

degree angle could be achieved between the buttock and back slats before

interference occurred, as seen in Figure 7-15. A sliding pivot was devised to

overcome this problem but was not viable because it required movement from an

extra actuator. Utilising a permanent gap between the zones solves the problem

but to achieve the desired 80 degrees would require all of the available 70mm.

Major developments in the back mechanism design at this stage allowed for a

separate head and back section, reducing the required angle of the back to 60

degrees to achieve a head adjustment of 90 degrees (Figure 7-16). To achieve this

reduced angle, a permanent clearance gap of only 45mm between the buttocks

and back sections is required, leaving 25mm for the remaining hinges and

clearances.

Further developments made the roller concepts looks unsuitable and as a result

the off the shelf fittings for retrofitting to the bed were revisited. The concepts

behind some of these designs were able to be adapted to the model being


76

developed. The Electro Lift plus adjustable bed by Franko (Figure 7-17) was

found to be a system that delivered adjustment close to that which was desired.

The dimensions and styling are vastly different but the general five bar linkage

mechanism can be adapted to meet the needs of the Design Mobel system. This

system gives the ability for one actuator to adjust both a back and head section

while keeping the system very simple.

Figure 7-15 Cross section view showing the interference of the slats as the back section

is raised

Figure 7-16 The modified back mechanism with reduced angle and clearance requirements


77

190mm 67deg

90deg

Buttocks

Leg

Head

Figure 7-17 The layout of the Franko lift plus system

7.3 Actuation

The source of the actuation controls the whole of the design of the adjustability

mechanism. Several different methods of actuation were investigated and this

section details the steps and decisions that were made.

Pneumatics System

A considerable amount of time was spent developing the initial concept of using

pneumatics to adjust the sections of the bed. The desire to avoid having

electricity running to the bed removed the possibility of using compressors for

supplying pressurised air. Development meetings were conducted with SMC

Pneumatics to determine the most appropriate system, which was found to be a

hydro-pneumatic concept (an air-oil system). In this approach a large reservoir

stores all the pre-pressurised air and oil so that when the valve is opened the

cylinder lifts up the bed section in a smooth fashion. The problem comes in

retracting the cylinder, which requires some effort from the occupier of the bed

who would have to force the raised section back down. The next problem

involves the varied weight of individuals, meaning that the force required to lift a

heavy person will be much greater than for a smaller person. The force required

to push the section back down again will be equal to this lifting force and thus

impossible for a smaller person to push down if it can lift the heavy man as well.

One solution is to make the driving force adjustable to the weight of the person


78

but this still requires the sections to be pushed down with effort. The other

possibility is to work the mechanism similar to that used for an adjustable office

chair where the weight is taken off the seat when it is raised. This means that a

much smaller force is required to lift the bed section and in turn it is much easier

to push back down. However, this is more difficult to perform when in a

reclining position than in a sitting position.

Yet another problem with this system is the expense involved. The retail price of

the cylinders required are approximately $200 each which almost exceeds the

budget before other parts and materials are even considered. In the end the

number of negative factors for this concept meant that it had to be put aside.

Unless some new technology is released or the price of the required items

decreases dramatically, such a system is not viable.

Gas Strut System

A gas strut works in much the same way as the proposed pneumatic system but

instead of pressurised air, high-pressurised gas is used in a sealed unit. This

means that the same force can be produced with a much smaller cylinder. The

gas strut has many advantages over the pneumatic system such as the reduced

size, the cost ($50 instead of $200) and the self-containment of the unit (no

reservoir or piping required). A major problem with both the gas strut and

pneumatic systems is the difficultly in controlling them in a simple and easy

manner. The controller that comes with the gas strut is an awkward cable system

so the idea of operating the trigger with a solenoid controlled by an electric hand

remote was conceived. This was the point at which the requirement of avoiding

electricity in the operation of the bed was reconsidered since the control and

operation desired would not be achievable with the current solutions. Electricity

was initially ruled out because of the danger of magnetic waves on the body,

however the magnitude of these waves can be minimised by using low voltages,

modifying and shielding the components involved. Many of the electrical


79

devices designed for the bed market have developed their products to European

standards for EMC (electromagnetic compatibility) and ESD (electrostatic

discharge). This led to the led to the elimination of the gas strut system as

electrically based solutions were pursued.

Electrical Actuators

With the possibility of using electricity now an option, electric actuators were

researched. Suppliers within New Zealand were approached and web based

searches were used to determine the possibilities that were available. Below is a

summary of the information that was found.

Linear Actuator

Linear actuators are devices that use electrical power to drive a shaft linearly up

and down and therefore can be used to actuate the bed’s adjustable sections.

Many different manufacturers make these linear actuators and they come in

many different shapes and forms. They differ mainly in the stroke length, the

force available, the power source (AC/DC), the durability, the mechanism, and

the general layout. The research uncovered a whole range of linear actuators

(examples shown in Figure 7-18) designed specifically for adjustable beds which

tend to be less robust than the industrial models but much more affordable and

suited for the purpose.

Using linear actuators has several disadvantages:

• They will protrude well below the bed frame as they extend

• A control box has to also be located and fixed to the frame

• The wires between the actuators and control box are untidy and unsafe

Using the specifications for the desired actuator and other factors such as size,

appearance and price, it was found the Gentact and Dewert models best suited

this application. There were two suitable models from Dewert: the Dymat and


80

Megamat shown in Figure 7-19. The Megamat is slightly more expensive but

faster with a greater load capacity and therefore was the model of choice. For

prototyping purposes, this model and the Gentact, a cheap Taiwanese Gentact

model, were purchased.

Figure 7-18 A selection of different actuators showing the difference in shape and form

Megamat Dymat

Figure 7-19 The Dewert linear actuators (reproduced from Dewert (2001))

Rotational Actuator

Linak produce a rotational actuator (Figure 7-20) that seemed like a very good

solution for the actuation requirements of the bed. Instead of having to convert

the linear motions of the actuator through a pivoting lever arm, a rotational

actuator can produce the rotational motion directly. When more detailed

specifications were found, it turned out that the device was larger than initially

perceived and was the same height as the side frame. The angle of movement

was limited to 85 degrees and the method of mounting was difficult. The


81

maximum speed it can produce (not even under load) is 0.56RPM and a complete

adjustment takes 40 seconds which is far to long. In the end this form of

actuation was eliminated because it did not prove to be what it initially

suggested it could be.

Figure 7-20 Linak Rotational Actuator (Reproduced from Linak (2001))

Duomat

Another type of actuator system by Dewert is the Duomat (Figure 7-21), an

actuator system that has all the motors and control units within the one

assembly. This means that there is no problem with untidy wires and trying to

mount the control box. Initially this type of actuator was not considered since

they were in common use by other bed manufacturers and was relatively big and

bulky. Their most attractive feature turned out to be that they were half the price

of the other linear actuators and would be easier to mount. To compare with the

linear actuators for prototyping purposes one of these actuators was also

purchased.

Figure 7-21 The Dewert Duomat actuator (reproduced from Dewert (2001))


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7.4 The Bed Features

This section looks at the decisions and development behind some of the more

specific parts of the adjustability mechanism.

Hinge

The purpose of the hinge is to create a point that two adjustable rail sections can

rotate about each other. Ideally an off the shelf item would be desired but there

are a number of constraints involved that make this impossible. Specially

designed hinges can be designed from plastic or aluminium to suit the rest of the

system. Many concepts were suggested but the most suitable option was a two

piece part that slides into the end of the extrusion and is fastened in place as in

Figure 7-22.

Figure 7-22 The leg hinge concept slotting into the adjustable rail

The position of the pivoting with regards to the adjustable rail is very important.

It is not possible to pivot exactly about the end of the rail or the two sides will

interfere (Figure 7-23). The rail can be cut away so that the interference is

removed (Figure 7-24) but the more that is cut away the more unpleasant it looks.

In all cases the groove for the shoe has to be complete and clear all the way to the

end of the rail for the shoes and spacers to sit comfortably.


83

Figure 7-23 Pivoting about the end of the rail causes interference

Figure 7-24 The rail can be cut away to stop interference

The alternative is to have the pivot point about the top or bottom the rail. The

pivot can be about the bottom edge for the knee hinge (Figure 7-25) and about the

top edge for the back and thigh hinges (Figure 7-26) but in both cases this leave a

dangerous finger jamming gap.

Figure 7-25 Bottom pivoting for knee joint

Figure 7-26 Top pivoting for back and thigh joint

To help in the safety of the hinge, a special protective cover such as a flexible film

that sits over the gap can be used. The other option is to include special slots on

the outside that cross the hinge and keep the gap covered as it slides in and out.

Cross Tube

The purpose of the cross tube is to deliver the torque from the actuator to the

mechanism resulting in the adjustment motion. To be able to rotate freely a bush

can be used to help reduce the friction and wear on the tube and contact points.


84

The cross tube can be mounted in a number of different variations, below are

some of the concepts that were developed.

• Pivot brackets that bolt onto the bed frame and mount the tube below the

level of the frame.

Figure 7-27 Pivot bracket used to mount the cross tube below the level of the frame

• To raise the cross tube into the frame, a bracket that holds the cross tube

and fastens directly onto the frame is used. This makes assembly of the

system easier because the subassembly is just dropped down and fastened

into place.

Figure 7-28 Pivot bracket that fastens directly to the sidewall to mount the cross tube

within the height of the bed frame

• Mount the cross tube straight into the frame to keep the system simple and

avoid the need for using any extra parts. This was the chosen method

because it was so simple with its only draw back being that the bar has to


85

be inserted during the assembly of the bed frame, which turned out to not

be as difficult as initially assumed.

Figure 7-29 Mounting the cross tube directly into the bed frame side wall

Fastening to The Frame

The adjustable rails and adjustable mechanisms have to be mounted to the bed

frame side rail but the aluminium wall is only 2.5mm thick (Figure 7-30) so that a

normal fastener just rips out when a large load is applied. The fasteners cannot

pass through the outer wall because this area has to remain untouched to

preserve the aesthetic form of the rail. Therefore some way had to be developed

to mount the parts to the inside wall of the extrusion.

Figure 7-30 Schematic of the bed frame side rail

Ideally all the fastening should be performed with the same type of fastener to

reduce the complexity and costs involved. The fastener should also be small,

unobtrusive, aesthetic and quick, easy, and cheap to manufacture and install.


86

The only off the shelf product that seemed to be suitable was a thin wall fastener

with an internal thread called a Rivnut as shown in Figure 7-31. The Rivnut is

inserted like a rivet with the end crumpled as it is drawn against the wall using a

pneumatic applicator. A sample piece of aluminium was tested with a rivnut but

it ripped away from the wall under even a small load.

Before After

Figure 7-31 Rivnut in a thin wall sheet

The fastener suppliers suggested developing a plate bracket (Figure 7-32) that

will strengthen the wall and distribute the load over several fasteners. This

bracket can either be screwed or riveted on to the bed frame and the devices

mounted to it through a centrally located thread.

Figure 7-32 Plate bracket for mounting devices to the bed frame

A suitable fastener was eventually discovered in the aircraft industry (Figure

7-33) but was far outside the allowable price range. The military type fastener

may be copied and developed for this project at a much more affordable price but

this was also scrapped when another stronger rivnut was sourced. Another

rivnut was sourced that was much stronger than the first one that was tested.

The rivnut was fastened to a test piece of aluminium and a series of weights were

hung off it from a bolt. A single rivnut was capable of holding over 80kg without


87

ripping out or deforming the bed frame. This rivnut was certainly the most

suitable solution considering its ability to withstand the loads while still being

very simple, cheap and unobtrusive.

Figure 7-33 The aircraft fastener is riveted to the aluminium sheet

Adjustable Rail Mounting

The adjustable rail has to be mounted to the bed frame and be allowed to rotate

freely to produce the desired adjustment. The simplest way to achieve this is to

allow it to rotate about a bolt that is fastened directly to the side rail. It is not

possible to have metal rubbing directly on the thin aluminium wall or the parts

will wear out too quickly and therefore a bush is used to distribute the load and

reduce the wear. The simple method of mounting that was developed using a

bolt and bush arrangement is shown in Figure 7-34.

Figure 7-34 Example of pivot mounting using a bolt and bush arrangement

A universal fastener was designed to fasten struts and other items to the

adjustable rails and allow them to rotate freely, as shown in Figure 7-35. The


88

fastener is held in place with a circlip and has a corresponding bush that acts as a

spacer to reduce friction between the strut and rail as well as distributing the

load over the fastener surface.

Figure 7-35 Adjustable rail attachment fastener

Actuator Mount

All the linear actuators investigated have clevis mounts and in this case they

mount directly to a lever arm that delivers the torque to the cross tube. If was

found that during the full motion of the actuator it was impossible to avoid

collisions with the lever. To overcome this problem a special yoke was designed

(Figure 7-36) that sits around the clevis head of the actuator allowing a much

greater range of motion.

Figure 7-36 Mounting the actuator clevis with a yoke attachment


89

Stoppers

The bed is held rigidly in place in the flat configuration using stoppers that take

up any excessive force applied to the mechanism. The stopper is made of a

material such as plastic or rubber to avoid noise when the rail is dropped down

on it. Doorstops were the closest off the shelf parts that would be suitable since

they can be relatively attractive, have a rubber coating to stop the noise and are

easily mounted to the bed frame. A Heaffle doorstop sample looked quite

suitable except it had a weak internal plastic mount. The internal mount could be

replaced by one manufactured from metal to increase the maximum possible

loading to make use of the attractive clip on rubber outer. The stoppers are

located, like the crossbars, away from the mounting points of the adjustable rails

sections as shown in Figure 7-37.

Figure 7-37 The location of the stopper I relation to the fixed buttocks

7.5 Back Mechanism

A new level in detail was achievable with the decision to develop a five bar

mechanism for the back section. The preliminary design of the back mechanism

was clarified and the mechanism of operation clairfied. The actuator moves the

head section up to an angle of 30 degrees and is locked in place with the back

section. As the actuator continues to lift the head, the back is also bought up to

an angle of 60 degrees as shown in Figure 7-38.

The locking is achieved with a peg that rests against the back rail and is mounted

to the back mechanism hinge. As the back hinge rotates the peg follows an arc,

taking it from resting on the rail, away from the rail and back to the rail to lock

the head section at the 30-degree extreme as seen in (Figure 7-39).


90

Minimum Configuration:

Head Max/Back Min:

Maximum Configuration:

Figure 7-38 Head section movement

Figure 7-39 The movement of the peg in the head hinge


91

To aid in the solving of the kinematics of the mechanism a piece of software

called ‘Five Bar’ was utilised. A screen shot of the software in use is shown in

Figure 7-40. The output from the programme gave valuable information on the

forces, torques and speeds of the linkages.

Figure 7-40 Screen shot of the kinematics software 5-Bar

With the development of the new 5 bar system, a back pivot was required to

provide the extra link to the mechanism as seen in Figure 7-41. Since all the parts

involved are made from steel, the pivot is easily manufactured from sheet and

welded to the cross tube. The longer the length of the pivot, the smaller the

rotation and force required, but this results in a pivot that protrudes well below

the frame.

Figure 7-41 Back pivot and cross rail


92

The final layout of the back mechanism assembly is shown in (Figure 7-42).

Figure 7-42 The final configuration of the back mechanism

7.6 Leg Mechanism

A simple four bar mechanism was developed for producing the bent leg

adjustment for the bottom mechanism (Figure 7-43). Since the motion was so

simplistic the roller concept was never considered. The actuator delivers the

movement to the strut in the same way as the back mechanism, with the rotation

of the crosstube.

↑

Figure 7-43 Leg 4 bar mechanism concept


93

Based on the factors already described a male/female hinge design was

developed within the size constraints that slots into the thigh and leg adjustable

rails (Figure 7-44).

Figure 7-44 The final design of the leg hinge

The final layout of the leg mechanism assembly is shown in (Figure 7-45) below.

↑

Figure 7-45 The final configuration of the leg mechanism


94

7.7 Summary

After many iterations of the subassemblies the preliminary design was

completed. The layout and form of this design turned out to be very simple and

aesthetically pleasing while still conforming to the requirements set out in the

PDS. The final method of actuation was still undecided but the system was easily

modified to accommodate the three systems since they all deliver the adjustment

through the rotation of the crosstube. Rotation of the top crosstube lifts the head

and back sections through the five bar linkage mechanism while the bottom

crosstube four bar linkages lift and bend the leg sections. A rendered view of the

final SolidWorks model is shown in Figure 7-46.

Figure 7-46 A rendered CAD model of the adjustable bed

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8 Prototype

With the completion of the preliminary design the concept was ready to be tested

with the production of a prototype. Once completed, the prototype was used to

perform a user trial to get information from the user on the performance and

appearance of the mechanism. The model was also scrutinised under a design

review to determine what changes had to be made.

8.1 Problems to Overcome in the Making of the Prototype

The prototype was used to compare and test three actuators to determine which

would be the most suitable for the final product: the Dewert Megamat, the

Dewert Duomat, and the Gentact linear actuator. The mechanism had to be

modified to accommodate the different actuators but since only one of these

actuator types would be used in the production model the design modifications

for this would only be relevant to the prototype. The two linear actuators used

the same mechanism but the Duomat had a varied mounting mechanism that

was much simpler.

Since the prototype is only a one off product it is not possible to create the parts

exactly as they would be made in production. This is a problem when one of the

critical parts is difficult and costly to make. The adjustable rails were an example

of this as they required the development of a tool for aluminium extrusion which

was considered not to be viable until the design was established. To overcome

this problem a rail had to be fabricated as close as possible to that of the final

production part shown in Figure 8-1. The solution that was pursued involved

creating an insert with the shoe groove cut into it and welding it into a

rectangular extrusion with its top cut off as seen in Figure 8-2.

A man who specialises in creating prototype models mocked up the plastic leg

hinges. The design turned out to be very safe as the hinge pushed the fingers out

rather than jamming as the gap closed up between the two halves. While the

Prototype

96

prototype was being assembled and the leg assembly motion was being tested,

the leg hinge broke. There was insufficient clearance between the thin walls and

were not tough enough for the side loads so they broke off. To solve this

problem quickly and at the same time introduce a new idea to reduce the number

of parts, a simple aluminium hinge similar to the male side of the plastic hinge

was developed. Instead of requiring two parts, a simple single cast hinge is used

with the female side removed and the axle sits in the wall of the adjustable rail

(Figure 8-3).

Figure 8-1 The desired adjustable rail extrusion

Figure 8-2 The final solution for the prototype adjustable rail

Figure 8-3 Single piece aluminium hinge

Prototype

97

8.2 Prototype User Trial

The prototype had been developed so that it was a working model capable of

performing a user trial. The main purpose of the trial was to gather information

from the participants on: their ability to use the bed, their perceptions of its

overall comfort and their opinions about the system. The specific questions that

need to be answered were as follows:

• Does the prototype perform to the levels set in the design specification?

• What is the users subjective reaction to the operation, structure and

aesthetics of the mechanism?

• Does the articulation positioning give the user a high level of comfort

under the various activities?

Methodology

The usability test consisted of four parts: and each participant took about 45

minutes to complete them:

1. Greeting and orientation

2. Pre-test Questionnaire: given to the user to determine first impressions of

the bed.

3. Performance Test: The participant was asked to perform three activities

(reading, watching television, and writing) on the bed and to rate these

activities for comfort between a flat and adjusted position. Ratings of

comfort were also directed at specific areas of the body: neck, arms, back,

buttock, leg and thighs.

4. Post-test questionnaire: given to the user to determine the performance,

operation and comfort of the bed.

A total of 19 participants, 10 male and 9 female (Table 8-1), were tested during

the week of September 24th, 2001 at the Harbour City motel conference room in

Tauranga. The participants came from an opportunity sample of people between

Prototype

98

the ages of 25-55 from businesses in the local area. The reading activity involved

giving the participants a book to read, postcards were given to the subjects to

perform the writing test, and a television was set up in 1.5m of the ground in

front of the bed for the television watching activity. The atmosphere was kept as

constant as possible for each participant and made as comfortable as allowable

within the limitations of the room. The participants were asked to make

themselves comfortable by removing any footwear and uncomfortable outer

clothing.

Table 8-1 The number of male and female participants in the user trial

Total 19

Male 10

Female 9 There were many potential limitations to the trial. Below are listed some of the

obvious limitations:

• Small sample size

• Unrepresentative data sample (gender, age socially, physically,

ethically)

• Effects of incentives to participate. A meal voucher to a local

restaurant was offered to each participant.

• Effects of clothing. Participants were not using their standard

sleepwear

• Limited length of time in each activity. Ideally the activities should be

performed for an extended time to overcome the initial comfort to

discover the true comfort

• Variations in the subject’s level of relaxation. Some people may have

been having a stressful day or the environment may cause some to be

more relaxed than others

• Time of day variations. The participants were tested at various times

of the day and this may cause them to be more or less relaxed.

• Participant nervousness affecting relaxation

Prototype

99

The Gentact linear actuators were used for the trial because the Dewert ones had

not arrived in time. The Duomat was the preferred actuator so the performance

of the bed was not as good as intended. This was taken into account in the

interpretation of the results. Photos of the prototype bed are shown from Figure

8-5 - Figure 8-10.

Results

The full summary of results is shown in Appendix K. The pre-test questionnaire

gave valuable information on the users first perception of the bed (Table 8-2).

Most people initially appear to be scared of using an adjustable bed but once they

give it a try they usually want to buy one for themselves. The average rating for

the appearance of robustness, simplicity to use, user friendliness, and general

interest were all very positive with ratings well above four out of five. The initial

appeal of the bed was not quite as high at 3.79±0.92 but was to be expected as

stated earlier.

Table 8-2 Pre-Questionnaire average ratings


Robust 4.32 0.58

Simple 4.42 0.69

Friendly 4.42 0.61

Appeal 3.79 0.92

Interest 4.32 0.75 Note: Ratings are out of 5 with 1 being the most negative and 5 being the most positive

Once the subjects became comfortable with using the bed they responded more

positively to performing the three activities (Table 8-3). The overall comfort of

adjusting the bed rose by 1.47±1.30 for reading, 1.21±0.77 for watching television

and 2.03±1.14 for writing. The subject’s perception of the support provided by

the bed also rose in similar proportions but not to the same extent.

In the case of watching television the neck has to be tilted forward to see the

screen and with writing the neck has to be even more bent forward. The adjusted

Prototype

100

bed seems to greatly aid the support and comfort of the neck with the greatest

benefits coming in writing and watching television (Reading =1.11±1.70, Writing

=1.50±1.46, Television =1.53±1.35). The back comfort is also greatly enhanced

through the adjustment of the bed for similar reasons (Reading =1.32±1.30,

Writing =1.24±1.51, Television =1.16±0.83).

The back angle was greatest when writing to give the head support and the body

a more upright stance (Reading =30.00±10.20deg, Writing =38.34±8.42deg,

Television =29.71±10.48deg). The maximum angle for the back was reached by

26% of participants when writing but only 10% for reading and 5% for television

watching (Table 8-4). A number of participants felt that their head sat above the

head zone and were unsupported, this tended to be the taller subjects with long

torsos. This was shown in the lower average rating of 3.61±1.09 for the head

support in the post questionnaire (Table 8-5) but a very a positive average rating

for the back adjustment of 4.29±0.80.

The increase in rating of the buttocks region is not as high as the back and neck

but it is still significant (Reading =0.92±1.42, Writing =0.74±0.87, Television

=0.84±1.17 from Table 8-3). The users tended to find that as they adjust the bed

upwards the buttocks region became more comfortable. There were some

exceptions to this though, with some who felt that as they moved into a more

seated position, more pressure was developed in the buttocks.

The increase in comfort to the legs was not nearly as significant as for the upper

body (Reading =0.68±1.00, Writing =1.08±1.00, Television =0.68±0.82 from Table

8-3) and many people did not even adjust the leg section much at all (Reading

=8.89±4.50deg, Writing =9.66±4.41deg, Television =0.68±0.82deg). The number of

people who adjusted the leg to the maximum position was similar to that of the

back, except in reading where the percentage was raised from 10% to 21% (Table

8-4). The greater the leg angle the more support given to the material being held

Prototype

101

in the lap of the subject and this was most popular in writing and reading rather

than television watching. Generally the satisfaction of the leg adjustment was

high and was confirmed in the post questionnaire with an average rating of

4.42±0.77 (Table 8-5). The main desire expressed by a number of the participants

was the possibility of having more angle available in the leg adjustment.

When questioned on the specifics of the mechanisms control the results were

very favourable with all the significant questions indicating positive responses

above 4.2 (Table 8-5). Two sample infrared remotes had not arrived in time for

the trial and would have only improved these results. The cord length problem

would be removed but the chances of loosing the remote would rise greatly.

The operation of the bed also seems to be adequate with all of the post

questionnaire responses giving average ratings of 4.7 and above (Table 8-5). The

only area that was not as high was the quietness, which had a reading of

3.97±0.95. The results of the mattress questioning gave mattress movement =

4.68±0.58 and mattress bunching = 4.53±0.61 suggesting that the mattress is

certainly adequate for the job.

Table 8-3 The results of performing the three activities in the flat and adjusted configurations

Reading

Flat Adjusted Difference

Activity Rating Std Dev Rating Std Dev Rating Std Dev t-Test

Comfort 3.03 1.11 4.50 0.60 1.47 1.30 0.0001

Support 3.58 1.12 4.42 0.53 0.84 1.29 0.0108

Neck 2.84 1.50 3.95 0.78 1.11 1.70 0.0109

Arms 3.13 1.08 4.34 0.75 1.21 1.10 0.0001

Back 3.05 1.22 4.37 0.70 1.32 1.30 0.0003

Buttocks 3.42 1.22 4.34 0.58 0.92 1.42 0.0110

Leg 3.84 0.83 4.43 0.70 0.68 1.00 0.0081

Thigh 3.84 0.90 4.58 0.61 0.74 1.15 0.0118

Back Angle 30.00 10.20

Leg Angle 8.89 4.50

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102

Writing



Comfort 2.26 1.10 4.29 0.56 2.03 1.14 0.0000

Support 3.00 1.29 4.34 0.47 1.34 1.23 0.0002

Neck 2.29 0.84 3.79 0.98 1.50 1.46 0.0003

Arms 2.47 0.96 3.97 0.72 1.50 1.07 0.0000

Back 2.68 1.29 3.92 0.95 1.24 1.51 0.0022

Buttocks 3.26 1.05 4.00 0.88 0.74 0.87 0.0017

Leg 3.32 1.11 4.39 0.59 1.08 1.00 0.0002

Thigh 3.47 0.96 4.34 0.67 0.87 1.05 0.0021


Leg Angle 9.66 4.41

Television



Comfort 3.50 0.83 4.71 0.45 1.21 0.77 0.0000

Support 3.68 1.16 4.71 0.45 1.03 1.23 0.0019

Neck 2.68 1.34 4.21 0.79 1.53 1.35 0.0001

Arms 3.47 1.07 4.61 0.59 1.13 1.10 0.0003

Back 3.37 0.96 4.53 0.61 1.16 0.83 0.0000

Buttocks 3.68 1.06 4.53 0.51 0.84 1.17 0.0056

Leg 3.95 0.62 4.63 0.50 0.68 0.82 0.0019

Thigh 3.95 0.62 4.63 0.47 0.68 0.77 0.0011


Leg Angle 6.18 3.82

Table 8-4 The proportions of participants who set the desired position to the

maximum allowable back and leg angles

Max Back Max Leg Activity Number % Number % Reading 2 10.53 4 21.05 Writing 5 26.32 5 26.32 Television 1 5.26 1 5.26

Prototype

103

Table 8-5 Post Questionnaire results


Head support 3.61 1.09

Back adjustment 4.29 0.80

Leg adjustment 4.42 0.77

Lumbar support 4.08 0.92

Adjustability

Bed side table reach 3.37 1.01

Ease of adjustment 4.89 0.32

Ease of button pushing 4.84 0.50

Ease of control reach 4.68 0.58

Obtaining desired angle 4.68 0.48

Ease of loosing control 2.53 1.12

Ease of using in the dark 3.16 1.12

Control length adequacy 4.53 0.84

Remote holder adequacy 4.21 0.79

Remote toughness 4.32 0.58

Control

Remote understanding 4.58 0.90

Adjustment speed adequacy 4.79 0.42

Smoothness of adjustment 4.84 0.37

Quietness of adjustment 3.97 0.95

How at ease is the operator? 4.89 0.32

How safe does it feel to operate? 4.89 0.32

Operation

How robust does it feel? 4.89 0.32

Mattress movement 4.68 0.58 Mattress

Mattress bunching 4.53 0.61

Conclusions

Even though the prototype was completed the day before the scheduled trials

and extensive fine-tuning was not possible, it lasted the three busy days of trials

without any problems. The bed worked better than anticipated and everyone

seemed to be happy with the performance it delivered. As the Gentact linear

actuators were used instead of the preferred Dewert actuators it was anticipated

Prototype

104

that the trial would have shown even larger scores had the preferred actuator

been available.

8.3 Design Review

After the trial it was possible to compare the different actuator models on the

prototype with the arrival of the Dewert actuators. It was found that the Duomat

was far superior in performance and was able to deliver a greater range of

movement, was quieter and faster than the other two. These features would

certainly have satisfied those subjects who were unhappy about these aspects

during the user trial. The Duomat is half the price and has a much simpler

mounting arrangement with a much cleaner look. The prototype confirmed the

belief that the Duomat would be the actuator of choice for the system.

The QFD chart was updated to include (Figure 8-4) the latest information. This

gave a good indication of how the prototype compares to the targets that were

set out at the start of the project. From the chart it was possible to see what areas

of the mechanism were adequate and which required more work to bring them to

the desired level. The only areas that did not reach the targets for user

evaluations were: the bed side table reach which can only be improved by using

a slide back mechanism (already ruled out), the ease of loosing the remote and

the remote holder which are both not big issues.

There were many more engineering characteristics that did not measure up but

this was because some of the expectations were unrealistic and had been based

on what seemed to be suitable at the creation of the initial QFD chart. The

desired speed of adjustment was set at 0.053ms-1 but the Duomat could only

deliver 0.044ms-1 which turned out to be a suitable adjustment speed. Any faster

than this and the movement becomes dangerous. The desired back angle was set

at 80 degrees, which only just missed at 76 degree and therefore is not an issue.

The movement delay was 0.25s longer than desired but this is almost

Prototype

105

insignificant and cannot be improved since it is mainly dependent on the off the

shelf actuator. Initially the ability to adjust the speed of operation was desired

but this option is not available with these standard actuators. The mattress

bunching height was also much higher than desired but the studies showed that

this was not a significant problem.

Figure 8-4 QFD chart 29/10/01

Prototype

106

A design review meeting for the adjustability mechanism was performed and as

with any prototype situation there were many problems that need to be

alleviated. A summary of the main proposed design changes and future steps to

be performed are summarised below:

• Fasteners:

o Make uniform throughout

o Make the circlip groove deeper so it doesn’t pop off

• Stoppers:

o Reposition the leg stopper

• Crosstube:

o Requires some sort of positioning spacer to stop lateral movement

• Back Hinge:

o Increase pegs size to avoid breakage

o Add another peg to stop backward movement of back section

• Buttocks slats:

o Need to have a bracket made to hold the slats in place on the bed

frame

• Shoes and Spacers:

o Tend to be pulled out and move around so require some sort of

method of clamping them in place. This may be incorporated into

the end caps.

During the user trial many of the taller people found that their heads tended to

stick out over the end of the bed with no support available. The positioning of

the adjustable sections is a problem because of the differences in the sizes of

people bodies; it is not possible to satisfy everyone on the same bed. Further

investigations has to be performed to determine whether the adjustable section

layout has to be changed, which would break the substantial constraint set out by

the 330mm slat spacing system. The ideal would be to have a compromised

layout that is suitable for the greatest number of people.

Prototype

107

Taking these changes into account a second prototype will be produced and

more extensive testing will be performed. This will need to include use over a

more extended time frame to test the durability and life of the parts. The bed will

be given to potential customers to trial over a few days to acquire comments and

recommendations on its performance. The design will also undergo cyclic testing

to confirm that it can withstand the loads over the length of its working life.

Prototype

108

Figure 8-5 Photo of the fully adjusted bed with mattress

Figure 8-6 Photo of the bed with a subject testing the adjustment

Prototype

109

Figure 8-7 Photo of the fully adjusted mechanism

Figure 8-8 Side on photo of the fully adjusted mechanism

Prototype

110

Figure 8-9 Close up photo of the prototype leg adjustment with mattress

Figure 8-10 Close up photo of the prototype leg hinge

111

9 Discussion

The aim of this project was to design an adjustable bed and to do so in a

systematic and methodical way. This chapter discusses some of the issues that

arose at each stage of the design process.

9.1 “Clarifying the Task” Step

It is essential when developing a product that the task is clearly defined. If the

task is not clarified the final product may not be entirely what the company

intended. Many design techniques were used to help clarify the problem

presented by Design Mobel and these techniques were very useful in

determining the functions and objectives required by the end product. This

formal framework was important in the way it stopped the designer from

rushing into solving the problem and potentially overlooking important aspects

of the final design. Even though using this framework caused the design process

to take longer than was desired, it provided the designer with confidence that the

design will closely match what the client had desired.

The brief that was presented by Design Mobel was too vaguely defined and

required much work to determine the specifics of what was wanted. The

company wanted to produce an adjustable bed but had not done any research to

find out what was required. As a result a large amount of research was

performed, involving analysis of patents and other products on the market, to

querying customers on what they would want from such a product. One

problem that arose from questioning customers was that many did not see the

product as a need until they actually tried the adjustable bed during user trials.

Nonetheless the interaction that was carried out with the end user during the

project lifted many of these customers past their preconceptions that adjustable

beds are just for use in hospitals, to viewing these beds as a desirable piece of

furniture to purchase.

Discussion

112

The final outcome from the clarifying phase was the creation of the preliminary

PDS document. This document was a living document that was never fully

complete because it continually changed and developed as more information was

gathered. At many stages during the project a point was reached that could not

be passed until a requirement or constraint was clarified or created and added to

the PDS. Nevertheless it was also important not to make the PDS too specific

without clarifying the necessity of the constraint and in doing removing a

number of very suitable designs. This was evident in the project with the

significant change in the direction of the design when the limitation of avoiding

the use of electrical devices was eliminated.

The ideal situation for a designer would be to be given a complete PDS, with the

only requirement being to solve the problem through design. The drawback with

this is that much of the information that was required from the customer could

not be gathered solely by marketing but required engineering knowledge.

However, some of the work that was completed during this project, such as

customer questionnaires, could have been performed by marketing personnel

who are experts in this area. This in turn would have saved the designer a

considerable amount of time.

9.2 “Concept Design” Step

The conceptual phase is considered the most demanding on the designer because

for the design to be successful a suitable concept must be developed. This phase

demands a great deal of creative ability and is very much open for things to go

wrong. To avoid such a possibility this stage of the project was strongly guided

by design techniques to help in the development and evaluation of the concepts.

It is hard to determine to what extent these techniques improved the final

outcome of the design, but the comment that can be made is that by using these

techniques a large number of possible concepts resulted, from which a very

successful final design was produced.

Discussion

113

The final concept that was developed turned out to be similar to the majority of

products already on the market. The range of possible design outcomes were

relatively narrow because the functions required could only be satisfied in a

small number of ways within the constraints.

Since the designer performed most of the project singularly, regular meetings

and general input from others was important. This input was valuable both for

the development of ideas but also in keeping the design heading in the right

direction as people with a more objective view of the situation were able to

contribute. The brainstorming sessions worked well and enabled people to

bounce their ideas off each other. It was interesting to note that there were many

good ideas developed during these group sessions but most of these ideas had

already been conceptualised by the designer. If the sessions were performed

within a group of people developing the product the sessions may have been of

more value. Conversely it can be good to get outsiders to be involved because

they can bring in new ideas that may not have been thought of by the designer

because he or she have become stuck in a single mind set.

The single synectics session did not prove to be very useful and the process

should be tried a few more times before any conclusions can be made on how

suitable synectics are as a design aid in this context. Many analogies were

suggested in the session but none of them seem to lead to any suitable new

concepts. This may be due to the nature of the project, since the number of

possible options may be very small and may have already been reached in the

brainstorming sessions. The other problem was that participants found it hard to

get into the right mind set to come up with the analogies and this may have been

due to the way the session were run, or the environment.

The list of concepts that were developed were then expanded utilising the

morphological matrix technique. This greatly expanded the list of possible

Discussion

114

solutions as planned but only a fraction of the concepts were actually worth

while investigating. Nonetheless, if this is what is required to generate even one

possible concept that may result in the principle solution, the time spent cannot

be seen as wasted. The way in which this technique was successful was in

making the designer consider every aspect of a concept before it was written off

as unsuitable. Since the system was already broken up into different functional

components it was quite easy to match them up to configurations that were

practical which in turn led to the flow of further ideas.

Looking back in retrospect the rating system that was used for the evaluation

should be changed. A lot more is now known about the system and other

additional materials have been collected so that the initial decisions that were

made during the conceptual phase would be quite different if performed at this

stage. The two concepts that were considered the highest rating by the

evaluation technique were later found to be less attractive than the ratings

suggested because of unforeseen complexity and costs. At the time, limited

knowledge was used to create a selection criteria that was not developed to a

level that eliminated these concepts. If the process were repeated at this time the

concept that was third in the evaluation, and the concept finally pursued, would

now be the top choice. Even so, the selection that was finally pursued would still

be the concept of choice if the evaluation was repeated at this time. When the

evaluation was performed it was based on the current PDS information. This

information was not necessarily mature enough to be used so the designer has to

be careful to make sure that the PDS has matured to a suitable level before

making serious design decisions from it.

It has to be accepted that sometimes the design process has to go down a dead

end in order for the designer to discover information that will direct the PDS in

the right direction. This was seen with the pneumatic concept. It was not until

detailed research had been performed that the idea was discovered to be

Discussion

115

unviable. A concept is still a loose idea until a feasibility study has been

performed to assess its suitability. Attractive features of the concept may not be

as simple and cost effective as were initially thought. The other possibility is that

at this stage the concept is not viable until new technology or new products are

released. For example if a very cheap pneumatic cylinder or some sort of human

operated pump was developed, the pneumatic system may suddenly became a

viable option.

9.3 “Embodiment Design” Step

The main purpose of the embodiment phase was to develop the idea generated in

the conceptual phase so that it could be developed for production. The

embodiment phase must not be overlooked. This is to avoid rushing into the

development of a product that may seem viable but will not perform as desired.

In this project the embodiment phase was investigated in much detail so that the

output design, even though still rough, was guaranteed to operate as intended.

During the embodiment phase the system was broken up into four distinct

subassemblies to keep the design work simple: the mechanism, the actuator, the

frame and the fastening. This was done to help make the distinction between the

embodiment and conceptual design phases more distinct. Each of the

subassemblies were at very different stages at any one point and their order

jumped around significantly during the development process. The frame and

method of actuation were quite developed at the onset of this phase but the

mechanism still required a great deal of work.

Each of these distinct areas had a huge effect on the other areas. This was seen

when the method of actuation was changed and the mechanism and the frame

had to be reworked and further developed to bring them back to the stage they

were at before the change. These iterations were quite frequent and the

subassembly required a design change whenever a stumbling block was reached.

Discussion

116

The large number of blocks that were reached and the resulting iterations became

quite frustrating because it felt like the design was constantly starting over again

and all the time spent going down one path had been wasted. While this was

true, once the changes were made and the new idea progressed it was usually

found that the number of steps taken back were not as many as originally

thought. The knowledge that was gained from the previous concept was hugely

valuable in developing information on what areas to develop and what to avoid

in further designs. In a sense this was a waste of time, but if this road had not

been taken a very innovative system may have bee missed out on.

The method of actuation first pursued in detail was the pneumatic system and

this was developed to the level of the embodiment phase before being dropped

for the gas strut. The gas strut proved to be essentially the same form of

actuation but in a much more simple, compact, and inexpensive form. The

problem with both of these concepts was that they violated the PDS in the area of

control and operation. None of the proposed concepts satisfied the PDS at this

point so the least damaging compromise had to be made. The collected

information suggested that the most suitable method of actuation would involve

electricity but this violated the requirement set out in the PDS. By opening this

constraint many other options became available that much more closely met the

targets set by the PDS requirements. The final actuation solution turned out to be

very suitable and had major benefits in regards to the frame and mechanism.

The mechanism went through much iteration that started with a roller design

and ended with a five bar linkage design. The changes to the frame were not

major but the number of mounting points and points of fastening were greatly

affected by the other two subassemblies.

Looking back, it would seem best to have gone straight to the final design and

ignored the other concepts. This is idealism since the path to the final design was

Discussion

117

a process, which involved the development of these concepts, which in turn

helped to bring forth the flow of ideas.

The development of the prototype from the preliminary design was very

beneficial because it provided a great deal of valuable information on the validity

of the developed concept. The user trial brought important feedback from the

customer to the new product. The physical model also helped to determine the

real design issues remaining and whether the design should move forward into

the detail design phase. The model also determined if the QFD targets and PDS

requirements were reached or if changes needed to be made to reach these.

These design changes will lead to a definitive design, which can be refined in the

detail design phase to develop the product for production. During this stage a

technique called value engineering will be used to help reduce the unnecessary

costs by bringing more value to the essential parts. The product will also be

developed further for manufacturing factors that will create a device that is ready

to be put into production.

118

10 Conclusions

The design of the adjustable bed was approached with a customer and

environmental focus, and in a systematic manner using the Pahl & Beitz

methodology. The process involved determining the design requirements,

creating concepts to solve these, and then building on the most promising design

with the goal of developing it for production.

Approaching the design in this manner meant that the phase of clarifying the

task was dwelt on for longer than would normally be expected but as a result the

problem was more fully defined. The design techniques forced the designer to

look at everything in far greater detail minimising the chance of overlooking

critical issues while they also helped to take a wider approach to the problem. As

a result the rest of the design process was performed with greater confidence

with the knowledge that the product would closely match what the client had

desired.

The framework of the Pahl and Beitz methodology for PDS provided the

opportunity to explore a variety of methods for creating solutions and evaluating

them which were very helpful in guiding the thought processes and keeping the

design on track.

The strengths and weaknesses of the methods became apparent and identified

the approaches that might be taken in any further development. One strength

was while the designer generated ideas individually, the addition of

brainstorming sessions helped to develop more concepts in a shorter time,

including ones that had been overlooked or not even considered. Some methods,

for example the synectics sessions, did not prove to be very useful. Under

different circumstances, with more experience and more extensive preparation

the technique might be more constructive. Due to the simplicity of the function

structures and design requirements some of the techniques including the

Conclusions

119

morphological matrix were somewhat limited in their potential. Using the

weighted objectives technique to select the principle solution was limited in

success because it was based on immature information. The solution that was

finally pursued was rated the third system in the selection technique because it

could not take into account information that was discovered later in the process.

Ideally the designer would want to start the design with the complete PDS from

the client, with the user, the marketing and the environmental requirements well

defined. Such an expectation is not reasonable, as much of the documentation

requires engineering knowledge and interpretation. It is critical in the design

process for the full development of the PDS not to be compromised, however

much time has to be devoted to it. Consequently the PDS document became a

living iterative document with changes and compromises made as further

information came to light. A large proportion of the knowledge came from

developing ideas that eventually turned out to be dead ends. Sometimes it was

one step forward and two back but with the subsequent realisation that it was the

information gained going down a sidetrack that provided the critical perspective

for development of other more fruitful ideas.

The outcome from the production of the prototype was very satisfactory. The

design review meeting that followed the testing and reporting of the first

prototype was very positive. The prototype that was produced met most of the

design requirements set out by Design Mobel. The design was able to meet the

very tight cost constraint of under $500 while still providing the level of style and

operation required. The solution was also successful in overcoming the difficult

constraints produced by the construction features of the Circadian bed frame.

A number of the wishes set out in the PDS were unmet but the only major

demand that was not achieved was the initial requirement to avoid the use of

electricity in the bed. Sometimes the client sets unrealistic demands and

Conclusions

120

constraints that conflict, or simply are not achievable within the engineer’s

framework. In this particular case the engineer had to compromise the electricity

requirement to provide the cheap and simplistic in-bed adjustment desired.

The prototype adjustable bed was successfully produced and tested with a better

than expected outcome. It would seem as this point that there will be only minor

design changes required to develop it for production levels. The next stage is to

fully develop the product in the detail design phase. This will include applying

the value engineering technique in order to bring more marketing value to the

product by removing any identifiable unnecessary costs. The final design goal is

to have the mechanism ready to be in production in August 2002, which at the

present time appears to be a very real possibility.

122

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Patent Analysis

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Appendix A Patent Analysis

Product Analysis

127

Appendix B Product Analysis

Product Analysis

128

Adjustability Activities Questionnaire

129

Appendix C Adjustability Activities Questionnaire The questionnaire listed in this section is the form that was sent to Design

Mobel’s valuable customers for important feedback on performing activities in

bed.

Customer Survey 12/2000 Gender:

1. Age (Optional):

2. We understand sleep is the primary purpose of a bed, however we often use a bed for other

activities. We would like to know what activities you do in bed apart from sleep, and what

activities you would like to be able to do but find difficult or cannot do because the bed limits

you.

Below is a list of some activities and space for adding any others. Could you

please indicate, by circling the appropriate number, how much you would like to

do the activity (the ‘Like’ column), how often you do it at the moment (the

‘Frequency’ Column), and how easy the task is to do in bed (the ‘Ease’ column).

If the activity does not apply to your situation, please leave it blank.

Like Frequency Ease

Activity Like Dislike Often Never Easy

Difficult

Read 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

Work/Study 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

Feed baby 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

Sickness 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comment:

Computer /

laptop 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Male Female


130

Comments:

Talk on the phone 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

Write 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

Eat 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

Watch television 5 4 3 2 1 5 4 3 2 1 5 4 3 2 1

Comments:

5 4 3 2 1 5 4 3 2 1 5 4 3 2 1 Other:

Comments:

5 4 3 2 1 5 4 3 2 1 5 4 3 2 1 Other:

Comments:

5 4 3 2 1 5 4 3 2 1 5 4 3 2 1 Other:

Comments:

3. What features could be added to a bed to improve functionality or performing the activities

listed on the previous page?

4. Do you sit or prop yourself up in bed?

What activities do you do this for?

Yes No


131

a. If you prop yourself up in bed, what method do you normally use?

Pillows

Moveable Headboard

Other:

b. How would you rate the satisfaction and comfort of this method?

Good Acceptable Bad

5 4 3 2 1

5. The following questions relate to adjustability in a bed frame.

a. If you could purchase a cost effective method of adjustability for a bed frame

would you see it as important that each person could adjust their surface

independently? (Ref diagram below)

Important Don’t mind Unimportant

5 4 3 2 1

Please Tick One

Please Circle One

Please Circle One


132

b. Please rank in order the types of adjustability you would prefer. (1 = lowest, 5 = highest)

Method of Adjustability Diagram Rank

Upright back with flat base

Back tilted with knee raised

Leg raised (Good for people with circulation problems)

Back and legs raised

Back and leg raised with knee bend.

6. If there is anything else you feel could improve the functionality of DM beds please

comment here:

Adjustability Activities Survey Summary

133

Appendix D Adjustability Activities Survey Summary

Bed Adjustability User Trial

134

Appendix E Bed Adjustability User Trial

Function Structures

135

Appendix F Function Structures Rough Structure:

→ User performs action to adjust bed section(s)

→ Particular

section(s) of the bed adjusts

→ User reaches

desired position




Refined Structure:

• Users motivation:

o Uncomfortable

o Wants to move into position suitable for a certain activity

o Wants to lie down

• Actuator stores power:

o Electricity

o Air

Compressed

Pumped

o Personal weight

o Personal energy

• User input:

o Electrical signal:

User presses a button →

Electrical Signal sent to

Actuator

o Pneumatic Valve:

User depresses valve →

Air is released and Actuator

moves

o Lever: User

pulls/pushes lever

→ Mechanism Actuated

o Button release:

User presses a button →

Mechanism unlocked to move freely

Function Structures

136

• Bed Section Adjusts:

o Actuator moves

o Mechanism moves under manual actuation

o Movement controlled by body movements and actuator

• Outcome:

o User moved to desired position

Total Structures:

1. Electrically powered Electricity Electricity

↓ ↓

→ User presses a button →

Electrical Signal sent to

Actuator → Actuator

moves → User reaches

desired position




2.Air powered

Compressed Air

↓

→ User

depresses valve

→

Air is released and

Actuator moves

→ User reaches

desired position




3.Personal weight powered

Human Effort

↓

→ User

pulls/pushes lever

→ Mechanism Actuated →

User moved to desired position




4.Personal energy powered

Human Effort

↓

→ User presses a button →

Mechanism unlocked to move freely

→ Mechanism moved →

User reaches desired position




QFD

137

Appendix G QFD This section gives a summary of the steps that were taken in the QFD procedure

and the results that were obtained.

1) Identify customer requirements in terms of product attributes.

a) Adjusted Position:

• Head/Neck support • Arm support

• Back adjustment • Lumbar support • Leg Adjustment • Bedside table reach

b) Control:

• Ease of use • Length of cord • Understanding • No cord • Force required to operate • Control Holder

• Ease of reaching the control • Fixed control • Ease of obtaining angle • Auto lower button • Ease of loosing remote • Programmable positions • Ease of using remote in dark • Hardiness of control

c) Operation:

• Speed • How at ease they felt

• Is the speed adjustable? • Safety • Smoothness • Robustness • Noise

d) Mattress:

• Does it move around? • Mattress bunching e) Situations:

• 1 up, 1 down • Cost appeal • Double bed

f) Extras:

• Built in light • Massage • Accessories socket • Support Surface

g) Activities:

• Reading • Phoning • Television watching • Computing • Working • Eating

2) Determine the relative importance of the attributes:

QFD

138

3) Evaluate the attributes of competing products:

• Distribute 500 points around the customer requirements to determine the

relative importance

• Rate the benchmarks from 0-10

• Table G-1 shows the evaluation of a normal bed and the Dico Adjustable

bed.

Table G-1 Evaluation of the attributes of a standard bed and the Dico Adjustable bed

Benchmarks Weighting Standard

Bed Dico Adj.

Bed

Head/Neck support 17 0 4.0

Back adjustment 35 0 5.0

Leg Adjustment 35 0 6.0

Arm support 10 0 3.0

Lumbar support 10 0 3.0 Adj

usta

bilit

y

Bedside table reach 10 0 4.0

Ease of use 6 0 8.1

Understanding 5 0 8.6

Force required to operate 8 0 8.8

Each of reaching the control 21 0 6.5

Ease of obtaining desired angles 21 0 8.4

Ease of loosing remote 2 0 2.0

Ease of using remote in dark 2 0 3.0

Length of cord 5 0 3.0

No cord 9 0 0.0

Control Holder 12 0 3.0

Fixed control 8 0 0.0

Auto lower button 16 0 0.0

Programmable positions 10 0 0.0

Con

trol

Hardiness of control 21 0 7.0

Speed 12 0 7.9

Is the speed adjustable? 4 0 0.0

Smoothness 12 0 9.0

Noise 12 10 9.2

Do they feel at ease? 15 10 9.0

Safety 20 10 8.4

Ope

ratio

n

Robustness 12 10 8.5

QFD

139

1 person up, 1 down? 6 0 8.0

A double bed? 5 10 7.0

Does mattress move around? 5 10 5.0

Mattress bunches 6 10 5.0 Situ

atio

ns

Cost appeal 5 10 3.0

Built in light 4 0 0.0

Accessories socket 3 0 0.0

Massage 2 0 0.0 Extr

as

Support Surface 5 0 0.0

Reading 28 5.5 8.5

Television watching 23 5.3 8.7

Working 15 4.4 7.9

Phoning 22 5.5 8.0

Computing 13 4.0 7.9

Act

iviti

es

Eating 16 4.5 6.8

4) Draw a matrix of product attributes against engineering characteristics.

• Table G-2 shows the table that was produced.

Table G-2 Engineering characteristics required for each of the requirements

Customer Requirement Engineering Characteristic Units

Head/Neck Max Angle o Head/Neck support

Head/Neck Max Velocity ms-1

Back Max Angle o Back adjustment

Back Max Velocity ms-1

Leg Max Angle o Leg Adjustment

Leg Max Velocity ms-1

Arm support Force taken off arm N

Lumbar support Force taken off lumbar support N

Adj

usta

bilit

y

Bedside table reach Distance from Wall to top bed end mm

Button Force N Ease of use Adjustment Inertia m4

Understanding Scale

Force required to operate Button Force N

Each of reaching the control Distance to storage position mm

Ease of obtaining desired angles Minimum adjustment o

Volume of remote cm3 Ease of loosing remote

Top Area of Remote cm2

Con

trol

Ease of using remote in dark Control button protrusion mm

Co

ntr

ol

Length of cord Cord length mm

QFD

140

No cord Y/N

Control Holder Y/N

Fixed control Y/N

Auto lower button Y/N

Programmable positions Y/N

Hardiness of control Remote impact resistance N (#)

All velocities ms-1 Speed

Movement delay s

Is the speed adjustable? Speed Range ms-1

Smoothness Scale

Noise Noise level db (#)

Do they feel at ease? Scale

Length of dangerous jamming area mm Safety

Collapsing Force N (#)

Ope

ratio

n

Robustness Collapsing Force N (#)

1 person up, 1 down? Scale

How does it handle a double bed? Scale

Force to move mattress N Does mattress move around?

Distance of mattress slip mm

Mattress bunches Height mattress bunches mm Situ

atio

ns

Cost appeal Scale

Built in light Y/N

Accessories socket Y/N

Massage Y/N Extr

as

Support Surface Scale

Head/Neck Max Angle o

Back Max Angle o

Reading

Leg Max Angle o

Television watching Head/Neck Max Angle o

Working Head/Neck Max Angle o

Phoning Back Max Angle o

Head/Neck Max Angle o Computing

Back Max Angle o

Head/Neck Max Angle o

Act

iviti

es

Eating

Back Max Angle o

QFD

141

The remaining steps involve the creation of the QFD chart which is shown in

Figure 5-6.

5) Identify the relationships between engineering characteristics and product

attributes.

6) Identify any relevant interactions between engineering characteristics.

7) Set target figures to be achieved for the engineering characteristics.

PDS

142

Appendix H PDS Table H-1 The PDS document issued on 10/10/2001

Design Mobel Requirements List

Adjustable Bed Mechanism

Issued on 10/10/2001

Changed D/W Requirements Frame Sizes:

5/6/01 D 2050x1530mm 5/6/01 D 2050x1630mm 5/6/01 D 2050x1730mm 5/6/01 D 2050x1830mm

Weight: W Low as possible for freights and assembly reasons Depth of Collapsed Bed: D <128mm Forces: D Max weight of user = 130kg D Shock loading from someone jumping on bed D No Deformation under loads Energy: W Avoid electricity or magnetic distortion W Any other power source available. Material: W Alloy for structural support W Recyclable plastics for brackets

10/6/01 W Steel for mechanism parts Control W Rapid adjustment over large distance W Fine adjustment W Reset button W Stored positions Operation: D In situ adjustment D Silent D Smooth controlled movement, not jerky D Intuitive controls for user, control icon based Safety: D Watch areas where people could catch hands between the frames

PDS

143

D Control system: Safe and away from problem areas D Stability D Movement limit. No chance of bed flicking up and hitting user D Likely degree of abuse should be considered D Definitive operating instructions must be prepared D Labelling should give adequate warnings.

19/3/01 D Length of dangerous jamming area max: 3500mm Ergonomics: D Initial user trial and questionnaires will form basis of ergonomic decisions

D Articulation points based on the initial load profile research: Divisions of 330mm slat zones.

Assembly: W Possible for the user to assemble unit to prevent high freight cost W Separate top and bottom half mechanism options Production: W Utilise pre-existing techniques of manufacture than developmental ones Preferred production methods: W Alloy or plastic extrusion W Injection moulding W High pressure die-casting Shipping and Packing:

D Primarily air freight, allow for sea freight. Thus allow for temperature changes.

D Card based, to protect mechanism and frame Maintenance: W No maintenance over 10 year operational time frame D Wear should relate to the 10 year timeframe W Easily removable maintainable parts Recycling:

D The product should utilise materials which are either recyclable or low impact

Costs: D Maximum permissible manufacturing costs = $300 per side D Cost of tooling: $60-80,000 Aesthetics, Appearance and Finish:

D Product should use existing product appearance as a basis to ensure consistency

PDS

144

W Semantically the product should take into account the nature of the bedroom. It should appear safe and robust to give the impression of durability

D Simple appearance

D Colour and finish of the parts will largely be determined in the basic system design

26/4/01 D Do not have holes on the outside of the frame Product Life Span: D 10 years before replacement or maintenance Market Constraints: D Electrical power supply D Power Active Near user Quantity: W 1000 units in the first year W Up to 5000 in 5 years Schedules: D End of date development for working prototype: 12/2001 D In production date: 8/2002 Target Customer: W Age: 25-45 W Weight: 60-90kg W Height: 1600-1910mm Operating Environment: D Designed to be used in the home bedroom D Temperature range: -10-50 oC D Affect of humidity on parts

19/3/01 Adjustability: 19/3/01 W Head/Neck support section max angle: >20o

29/10/01 W Back support section max angle: >75o 19/3/01 W Leg support section max angle: 36o 19/3/01 D Minimum Adjustment: 3mm

29/10/01 All velocities 0.044ms-1

19/3/01 Control Device: 19/3/01 D Button Force: 3/10 19/3/01 W Distance of remote to bed centre max: ½ width 19/3/01 W Volume of Remote: >160cm3 19/3/01 W Front Area of Remote: >70cm2 19/3/01 D Button Protrusion min: 2.5mm 19/3/01 D Remote cord length max: 2200mm 19/3/01 D Remote Toughness: 8/10

PDS

145

19/3/01 Mechanism: 19/3/01 D Movement Delay: 0.5s 19/3/01 W Speed Range: 0.05ms-1 19/3/01 D Noise Level: 2/10 (Dico = 4)

19/3/01 Structure: 19/3/01 D Inertia: 5/10 (Dico = 6) 19/3/01 D Collapsing Force: 8/10 (Dico = 6)

19/3/01 Mattress: 19/3/01 W Force to move mattress: 8/10 (Dico = 5) 19/3/01 D Distance of Mattress Slip: 10mm 19/3/01 D Mattress Bunching Height: 10mm

Replaces issue of 10/6/2000

Morphological Matrix Method

146

Appendix I Morphological Matrix Method

This section shows the steps that were taken in the morphological chart process

for generating concept alternatives.

1. List the features or functions that are essential to the product: Top Adjustment Power Leg Adjustment Integration Mechanism Other Features

Other: Safety In situ, easy to use Control Smooth, Silent Operation

2. For each features or function list the means by which it might be achieved:

• Top Adjustment: None Head/Back Head Contour Back

• Leg Adjustment: None Leg Bent Not Parallel Leg Contour Leg Bent Parallel

• Mechanism: Linkages Pivoting Sections Pulleys and wires Screw drive Pneumatic Cylinders Scissors Mechanism Dynamic Circular/linear gear Manual hinges Cams

• Power: Electric Air Bladder Gas Strut Personal Weight Pneumatic Manual move

• Integration: Fully assembled frame Assemble onto bed frame Separate 1/3 2/3 frame

• Other Features: Built in lamps Slide back mechanism Foldaway armrests


147

3. Draw up a chart containing all the possible sub-solutions (Table I-1):

Table I-1 List of all the possible means to achieve each of the features and functions

Cam

s

Link

ages

Scis

sors

Scre

w D

rive

Pulle

ys/

Wir

es

Man

ual

Man

ual

mov

e

Dyn

amic

Air

Bl

adde

r

Hea

d /B

ack

Leg

Bent

NP

Pneu

mat

ics

Com

p A

ir

All

Asm

Slid

e ba

ck

Back

Leg

Bent

P

Pivo

t Lev

er

Arm

Pers

onal

W

eigh

t

Som

e A

sm

Fold

away

ar

mre

sts

Hea

d

Leg

Stra

ight

Cir

cula

r /l

inea

r gea

r

Elec

tric

Sepa

rate

1/3

2/

3 fr

ame

Built

in

lam

ps

Mea

ns

Non

e

Non

e

Non

e

Non

e

Full

Fram

e

Non

e

Asm

= A

ssem

bly

Feat

ure

Top

Adj

.

Leg

Adj

.

Mec

hani

sm

Act

uatio

n

Inte

grat

ion

Acc

esso

ries

Not

es:


148

4. Identify feasible combinations of sub-solutions (Table I-2):

Table I-2 Morphological list of feasible solutions for each of the features and

functions No. Description Top Adj LegAdj Mechanism Power Integration Features

0.1 Normal Bed None None None None Full None

0.2 Dico Bed Back Leg Bent P

Pivot Arm

Electric Full None

1.1 Air Simple 1 Back Leg

Straight None Air

Bladder Full None

1.2 Air Simple 2 Back Leg Straight

None Air Bladder

1/3 & 2/3

None

1.3 Air Mid 1 Back Leg Bent P

None Air Bladder

Full None

1.4 Air Mid 2 Back Leg Bent P

None Air Bladder

1/3 & 2/3

None

1.5 Air Mid Asm Back Leg Bent P

None Air Bladder

All None

1.6 Air Duluxe 1 Back /Head

Leg Bent NP

None Air Bladder

Full None

1.7 Air Duluxe 2 Back /Head

Leg Bent NP

None Air Bladder

1/3 & 2/3

None

1.8 Air Duluxe Asm

Back /Head

Leg Bent NP

None Air Bladder

All None

2.1 Cam Elec

Simple 1 Back Leg

Straight Cam Electric Full None

2.2 Cam Elec Simple 2

Back Leg Straight

Cam Electric 1/3 & 2/3

None

2.3 Cam Elec Mid 1

Back Leg Bent P

Cam Electric Full None

2.4 Cam Elec Mid 2

Back Leg Bent P


None

2.5 Cam Elec Mid Asm

Back Leg Bent P

Cam Electric All None

2.6 Cam Elec Duluxe 1

Back /Head

Leg Bent NP

Cam Electric Full None

2.7 Cam Elec Duluxe 2

Back /Head

Leg Bent NP


None

2.8 Cam Elec Duluxe Asm

Back /Head

Leg Bent NP

Cam Electric All None

3.1 Cam Man

Simple 1 Back Leg

Straight Cam Manual Full None


149

3.2 Cam Man Simple 2

Back Leg Straight

Cam Manual 1/3 & 2/3

None

3.3 Cam Man Mid 1

Back Leg Bent P

Cam Manual Full None

3.4 Cam Man Mid 2

Back Leg Bent P


None

3.5 Cam Man Mid Asm

Back Leg Bent P

Cam Manual All None

3.6 Cam Man Duluxe 1

Back /Head

Leg Bent NP

Cam Manual Full None

3.7 Cam Man Duluxe 2

Back /Head

Leg Bent NP


None

3.8 Cam Man Duluxe Asm

Back /Head

Leg Bent NP

Cam Manual All None

4.1 Linkages Man

Simple 1 Back Leg

Straight Linkages Manual Full None

4.2 Linkages Man Simple 2

Back Leg Straight

Linkages Manual 1/3 & 2/3

None

4.3 Linkages Man Mid 1

Back Leg Bent P

Linkages Manual Full None

4.4 Linkages Man Mid 2

Back Leg Bent P


None

4.5 Linkages Man Mid Asm

Back Leg Bent P

Linkages Manual All None

4.6 Linkages Man Duluxe 1

Back /Head

Leg Bent NP

Linkages Manual Full None

4.7 Linkages Man Duluxe 2

Back /Head

Leg Bent NP


None

4.8 Linkages Man Duluxe Asm

Back /Head

Leg Bent NP

Linkages Manual All None

5.1 Scissor

Man Simple 1 Back Leg

Straight Scissor Manual Full None

5.2 Scissor Man Simple 2

Back Leg Straight

Scissor Manual 1/3 & 2/3

None

5.3 Scissor Man Mid 1

Back Leg Bent P

Scissor Manual Full None

5.4 Scissor Man Mid 2

Back Leg Bent P


None

5.5 Scissor Man Mid Asm

Back Leg Bent P

Scissor Manual All None

5.6 Scissor Man Duluxe 1

Back /Head

Leg Bent NP

Scissor Manual Full None

5.7 Scissor Man Duluxe 2

Back /Head

Leg Bent NP


None


150

5.8 Scissor Man Duluxe Asm

Back /Head

Leg Bent NP

Scissor Manual All None

6.1 Screw Elc

Simple 1 Back Leg

Straight Screw Electric Full None

6.2 Screw Elc Simple 2

Back Leg Straight

Screw Electric 1/3 & 2/3

None

6.3 Screw Elc Mid 1

Back Leg Bent P

Screw Electric Full None

6.4 Screw Elc Mid 2

Back Leg Bent P


None

6.5 Screw Elc Mid Asm

Back Leg Bent P

Screw Electric All None

6.6 Screw Elc Duluxe 1

Back /Head

Leg Bent NP

Screw Electric Full None

6.7 Screw Elc Duluxe 2

Back /Head

Leg Bent NP


None

6.8 Screw Elc Duluxe Asm

Back /Head

Leg Bent NP

Screw Electric All None

7.1 Pulley/Wire

Elc Simple 1 Back Leg

Straight Pulley /Wire

Electric Full None

7.2 Pulley/Wire Elc Simple 2

Back Leg Straight

Pulley /Wire

Electric 1/3 & 2/3

None

7.3 Pulley/Wire Elc Mid 1

Back Leg Bent P

Pulley /Wire

Electric Full None

7.4 Pulley/Wire Elc Mid 2

Back Leg Bent P

Pulley /Wire

Electric 1/3 & 2/3

None

7.5 Pulley/Wire Elc Mid Asm

Back Leg Bent P

Pulley /Wire

Electric All None

7.6 Pulley/Wire Elc Duluxe 1

Back /Head

Leg Bent NP

Pulley /Wire

Electric Full None

7.7 Pulley/Wire Elc Duluxe 2

Back /Head

Leg Bent NP

Pulley /Wire

Electric 1/3 & 2/3

None

7.8 Pulley/Wire Elc Duluxe Asm

Back /Head

Leg Bent NP

Pulley /Wire

Electric All None

8.1 Pulley/Wire

Man Simple 1 Back Leg

Straight Pulley /Wire

Manual Full None

8.2 Pulley/Wire Man Simple 2

Back Leg Straight

Pulley /Wire

Manual 1/3 & 2/3

None

8.3 Pulley/Wire Man Mid 1

Back Leg Bent P

Pulley /Wire

Manual Full None

8.4 Pulley/Wire Man Mid 2

Back Leg Bent P

Pulley /Wire

Manual 1/3 & 2/3

None

8.5 Pulley/Wire Man Mid Asm

Back Leg Bent P

Pulley /Wire

Manual All None


151

8.6 Pulley/Wire Man Duluxe 1

Back /Head

Leg Bent NP

Pulley /Wire

Manual Full None

8.7 Pulley/Wire Man Duluxe 2

Back /Head

Leg Bent NP

Pulley /Wire

Manual 1/3 & 2/3

None

8.8 Pulley/Wire Man Duluxe Asm

Back /Head

Leg Bent NP

Pulley /Wire

Manual All None

9.1 Circ/Lin Elec

Simple 1 Back Leg

Straight Circ /Lin

Electric Full None

9.2 Circ/Lin Elec Simple 2

Back Leg Straight

Circ /Lin

Electric 1/3 & 2/3

None

9.3 Circ/Lin Elec Mid 1

Back Leg Bent P

Circ /Lin

Electric Full None

9.4 Circ/Lin Elec Mid 2

Back Leg Bent P

Circ /Lin

Electric 1/3 & 2/3

None

9.5 Circ/Lin Elec Mid Asm

Back Leg Bent P

Circ /Lin

Electric All None

9.6 Circ/Lin Elec Duluxe 1

Back /Head

Leg Bent NP

Circ /Lin

Electric Full None

9.7 Circ/Lin Elec Duluxe 2

Back /Head

Leg Bent NP

Circ /Lin

Electric 1/3 & 2/3

None

9.8 Circ/Lin Elec Duluxe Asm

Back /Head

Leg Bent NP

Circ /Lin

Electric All None

10.1 Dynamic

Simple 1 Back Leg

Straight Dynamic P Weight Full None

10.2 Dynamic Simple 2

Back Leg Straight

Dynamic P Weight 1/3 & 2/3

None

10.3 Dynamic Mid 1

Back Leg Bent P

Dynamic P Weight Full None

10.4 Dynamic Mid 2

Back Leg Bent P


None

10.5 Dynamic Mid Asm

Back Leg Bent P

Dynamic P Weight All None

10.6 Dynamic Duluxe 1

Back /Head

Leg Bent NP

Dynamic P Weight Full None

10.7 Dynamic Duluxe 2

Back /Head

Leg Bent NP


None

10.8 Dynamic Duluxe Asm

Back /Head

Leg Bent NP

Dynamic P Weight All None

11.1 Manual

Simple 1 Back Leg

Straight Manual Manual Full None

11.2 Manual Simple 2

Back Leg Straight

Manual Manual 1/3 & 2/3

None

11.3 Manual Mid 1

Back Leg Bent P

Manual Manual Full None


152

11.4 Manual Mid 2

Back Leg Bent P


None

11.5 Manual Mid Asm

Back Leg Bent P

Manual Manual All None

11.6 Manual Duluxe 1

Back /Head

Leg Bent NP

Manual Manual Full None

11.7 Manual Duluxe 2

Back /Head

Leg Bent NP


None

11.8 Manual Duluxe Asm

Back /Head

Leg Bent NP

Manual Manual All None

12.1 Pivot Arm

Simple 1 Back Leg

Straight Pivot Arm

Electric Full None

12.2 Pivot Arm Simple 2

Back Leg Straight

Pivot Arm

Electric 1/3 & 2/3

None

12.3 Pivot Arm Mid 1

Back Leg Bent P

Pivot Arm

Electric Full None

12.4 Pivot Arm Mid 2

Back Leg Bent P

Pivot Arm

Electric 1/3 & 2/3

None

12.5 Pivot Arm Mid Asm

Back Leg Bent P

Pivot Arm

Electric All None

12.6 Pivot Arm Duluxe 1

Back /Head

Leg Bent NP

Pivot Arm

Electric Full Slide Back

12.7 Pivot Arm Duluxe 2

Back /Head

Leg Bent NP

Pivot Arm

Electric 1/3 & 2/3

Slide Back

12.8 Pivot Arm Duluxe Asm

Back /Head

Leg Bent NP

Pivot Arm

Electric All Slide Back

13.1 Pneumatic

Simple 1 Back Leg

Straight Pneumatic Comp

Air Full None

13.2 Pneumatic Simple 2

Back Leg Straight

Pneumatic Comp Air

1/3 & 2/3

None

13.3 Pneumatic Mid 1

Back Leg Bent P

Pneumatic Comp Air

Full None

13.4 Pneumatic Mid 2

Back Leg Bent P

Pneumatic Comp Air

1/3 & 2/3

None

13.5 Pneumatic Mid Asm

Back Leg Bent P

Pneumatic Comp Air

All None

13.6 Pneumatic Duluxe 1

Back /Head

Leg Bent NP

Pneumatic Comp Air

Full Slide Back

13.7 Pneumatic Duluxe 2

Back /Head

Leg Bent NP

Pneumatic Comp Air

1/3 & 2/3

Slide Back

13.8 Pneumatic Duluxe Asm

Back /Head

Leg Bent NP

Pneumatic Comp Air

All Slide Back

Evaluating Alternatives

153

Appendix J Evaluating Alternatives The following is a list of the steps taken to evaluate the concepts using the

weighted objectives techniques:

1. List the design objectives: Table J-1

Table J-1 Design objectives

Integration into bed frame (A) Assembly: Easy assembly by customer (B) As much assembly by customer as possible (C) Form: Simple and aesthetically pleasing to the eye (D) Adequate adjustability for activities (E) Minimum of parts (F) Energy source issues (G) Innovative (H)

Safety (I) Production/Manufacturing: Cheap (J) Availability of parts (K) Materials (L) Operation: Smooth (M) In situ adjustment (N) Shipping Issues (size) (O)

Maintenance: Easy Maintenance (P) No Maintenance Required (Q)


154

2. Rank-order the list of objectives: see Table J-2

Table J-2 Scores for each of the objectives.

Score Objective

0 A 1 D 2 E 4 N 5 H 6 J 7 I 8 C 9 M

10 K,O 11 B,F,G 13 L,Q 15 P

3. Assign relative weights to the objectives: see Table J-3

Table J-3 Objectives ranked in order and given weightings

Objective Weightings

A 13.50 D 12.00 E 11.00 N 10.00 H 9.50 J 8.00 I 7.00 C 6.75 M 5.00 O 4.50 K 4.00 G 3.50 B 2.00 F 1.50 Q 1.00 L 0.50 P 0.25

Total 100


155

4. Establish performance parameters or utility scores for each of the objectives:

see Table J-4.

Table J-4 The performance parameters for each of the objectives

Objective Performance Parameters

A Ease of Integration D Simplicity and Aesthetics of form

E Level of Adjustability

N Ease of adjusting from the bed

H Level of innovation

J Costs involved with manufacture

I Level of safety

C Percentage of assembly by the customer

M Smoothness of operation

O Size of packaging

K Availability of parts

G Energy Impact on Occupant

B Ease of assembly by customer

F Number of parts

Q Level of Maintenance required

L Commonality of materials

P Ease of maintenance

5. Calculate and compare the utility values of the alternative designs: The

summary results of this process are shown in Table 6-3.

Prototype User Trial

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Appendix K Prototype User Trial

04 01 004%20 %20masterate%20dissertation

Documents

design requirements

final design

design phase

design mobel team

number of design techniques

adjustable bed market

simple adjustable bed

bar linkage mechanism